U.S. patent number 3,622,702 [Application Number 04/789,841] was granted by the patent office on 1971-11-23 for tape reader and control system.
This patent grant is currently assigned to General Electric Company. Invention is credited to John J. Larew, Paul J. Moran.
United States Patent |
3,622,702 |
Larew , et al. |
November 23, 1971 |
TAPE READER AND CONTROL SYSTEM
Abstract
A system providing for improved local and remote control over
operation of a tape reader. The controls being operative to
selectively initiate and automatically terminate both the reading
and omission of data, with the omission operations being effected
at a higher rate than the reading operations. These controls also
being operative to automatically inhibit reading operations for
various time intervals when the unit is supplying a teleprinter and
particular mechanical commands are being executed by the
teleprinter.
Inventors: |
Larew; John J. (Waynesboro,
VA), Moran; Paul J. (Waynesboro, VA) |
Assignee: |
General Electric Company
(N/A)
|
Family
ID: |
25148829 |
Appl.
No.: |
04/789,841 |
Filed: |
January 8, 1969 |
Current U.S.
Class: |
178/17R; 400/63;
400/50; 400/73 |
Current CPC
Class: |
B41B
27/14 (20130101); B41B 27/10 (20130101); G06F
3/06 (20130101); B41B 25/00 (20130101); B41J
5/38 (20130101); B41J 3/50 (20130101); G06K
1/04 (20130101); B41B 27/00 (20130101) |
Current International
Class: |
B41J
5/31 (20060101); B41J 5/38 (20060101); B41J
3/50 (20060101); B41B 25/00 (20060101); B41J
3/44 (20060101); B41B 27/00 (20060101); B41B
27/10 (20060101); B41B 27/14 (20060101); G06F
3/06 (20060101); G06K 1/04 (20060101); G06K
1/00 (20060101); H04l 017/12 () |
Field of
Search: |
;178/17,17A,17B,23,23.1,79,80,81,17.5 ;197/20
;340/174.1A,174.1K |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: D'Amico; Tom
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. A tape reader and control system comprising gating means
controlling the response of the system to the reading of characters
on a tape, decoding means operative to detect a character on said
tape and provide discrete indications representative of said
character, means responsive to said decoding means for enabling
said gating means in accordance with the particular character
detected; and delay means responsive to the detection of at least
one previous predetermined character on said tape for delaying
enablement of said gating means in accordance with said previously
detected predetermined character.
2. A tape reader control system according to claim 1 wherein said
delay means is effective to introduce a long delay in response to
detection of at least one previously detected predetermined
character and a short delay in response to detection of at least
another one previously detected predetermined character.
3. A tape reader and control system according to claim 1, further
comprising first and second delay means controlled by said decoding
means to effect long or short delays, respectively, before
enablement of said gating means and depending upon a plurality of
previously detected characters.
4. A tape reader and control system according to claim 3 wherein
said first delay means is operative in response to detection of any
one of a plurality of nonprintable characters, and said second
delay means is operative in response to detection of a given one of
said plurality of nonprintable characters only if there has not
been a printable character since the detection of the previous
given one of a plurality of nonprintable characters.
5. A tape reader and control system according to claim 4 wherein
said plurality of characters comprises commands for mechanical
operations of connected equipment, and a second plurality of
characters comprises commands for printing particular characters at
said connected equipment, said second delay means being operative
in response to detection of a character of said second plurality
between the detection of a given one of said plurality of
nonprintable characters and the detection of the previous given one
of said plurality of nonprintable characters.
6. Apparatus according to claim 1 further comprising means
responsive to the detection of at least one subsequently presented
predetermined character on said tape for inhibiting the delayed
enablement of said gating means in accordance with said at least
one previous character detected.
7. Apparatus according to claim 24 wherein said third interval is
less than said first or second interval.
8. A tape reader and control system connected to a teleprinter,
said tape reader being operative in steps to read printable and
nonprintable tape bearing characters for controlling said
teleprinter, first means for detecting particular characters
requiring nonprinting operations of said teleprinter, control means
for automatically advancing the tape in said reader, delay means
operative in response to said first means to inhibit operation of
said control means for a first period of time sufficient for the
carrying out of said nonprinting operations, means for selectively
advancing the tape in discrete steps and presenting successive
characters for reading at each step, said means being selectively
inactivated upon detection of particular characters, and means
responsive to detection of a predetermined particular character to
inhibit the tape reader from reading at least one printable
character subsequently presented.
9. A tape reader and control system according to claim 8 including
means for advancing said reader at an accelerated rate during
detection of said at least one subsequently presented
character.
10. A tape reader and control system according to claim 8 wherein
said means is automatically activated upon detection of a
preselected character.
11. In a tape reader and control system connected to a teleprinter,
said tape reader being operative to advance the tape in discrete
increments in response to a signal, each increment placing a
successive code on the tape in a reading position, wherein said
codes represent printable characters and commands to said
teleprinter for printing said characters individually, in words,
and in lines; the improvement comprising first means for generating
said signal one time, gating means for providing said signal under
control of said teleprinter, detecting means for detecting the code
appearing in said reading position and providing discrete signal
conditions upon each advance of said tape and when said code
represents the end of a word or line, means operative to actuate
said first means and for selectively blocking said gating means
under the control of said discrete signal conditions.
12. In a tape reader and control system according to claim 11 means
operative when said gating means is blocked to supply said signals
to said reader at a high repetition rate.
13. In a tape reader and control system according to claim 11,
means operative to deactivate the tape reader when said detecting
means does not provide a discrete signal condition upon an advance
of the tape.
14. In a tape reader and control system according to claim 11,
means for periodically producing second signals that backspace the
tape in discrete increments in response to each signal, said means
being operative in response to a signal condition from the
teleprinter, means for terminating production of said second
signals when a second particular code is in said reading position,
and thereafter activating said first means.
15. A tape reader and control system according to claim 14, wherein
said second signals are produced at a high repetition rate.
16. A source of information in bit parallel, character serial form,
means for providing a first advance signal, means for reading out
of said source one character at a time in response to said first
advance signal, a printer, means for activating said printer to
respond to read characters, said means for providing a first
advance signal comprising means to generate a first advance signal
for enabling the reading of the next character after the printer
response is completed, means responsive to a read character being a
printable character for enabling said printer to respond to said
read character, means responsive to said read character being one
of a plural number of nonprintable characters for enabling said
printer to respond to said read, one of a plural number of
nonprintable characters and to generate a second advance signal for
reading the next character only after a given time delay, said
means for reading responsive to said second advance signal in place
of said first advance signal to read out the next character.
17. A source of information in bit parallel, character serial form,
means for reading out of said source one character at a time in
response to a control signal, a printer adapted to be enabled to
respond to such read characters, means responsive to a read
character being a printable character for enabling said printer to
respond to said read, printable character and to provide a first
control signal upon the response being completed, said means for
reading responsive to said first control signal for reading the
next character after the elapse of a first time period, means
responsive to said read character being one of a plural number of
nonprintable characters for enabling said printer to respond to
said read, one of a plural number of nonprintable characters and to
provide a second control signal upon the response being completed,
said means for reading responsive to said second control signal for
reading the next character only after the elapse of a second time
period, said means for reading responsive to said second control
signal in place of said first control signal to read out the next
character.
18. A source of information stored on tape in bit parallel,
character serial form, a tape reader, means for presenting one
character at a time from said source to said reader in response to
a control signal, a printer adapted to be enabled to respond to
such presented characters, means responsive to a presented
character being a printable character for enabling said printer to
respond to said presented, printable character and to provide a
first control signal upon the response being completed, said reader
responsive to said first control signal for reading the next
character, means responsive to said presented character being any
one of a plural number of nonprintable characters for enabling said
printer to respond to said presented, one of a plural number of
nonprintable characters and to provide a second control signal upon
the response being completed, and said reader responsive to said
second control signal for reading the next character only after a
given time delay.
19. A source of characters in digital form, means for presenting
one character at a time from said source in response to a control
signal, a printer adapted to be enabled to respond to such
presented characters, means responsive to a presented character
being a printable character for enabling said printer to respond to
said presented, printable character and to provide a first control
signal upon the response being completed, said means for presenting
responsive to said first control signal for presenting the next
character, means responsive to said presented character being one
of a plural number of nonprintable characters for enabling said
printer to respond to said presented, one of a plural number of
nonprintable characters and to provide a second control signal upon
the response being completed, and said means for presenting
responsive to said second control signal for presenting the next
character only after the elapse of a given time delay.
20. A tape reader and control system connected to a teleprinter,
said tape reader being operative in steps to read tape bearing
characters for controlling said teleprinter, first means for
detecting particular characters requiring mechanical operations of
said teleprinter, control means for automatically advancing the
tape in said reader, delay means operative in response to said
first means to inhibit operation of said control means for a first
period of time sufficient for the carrying out of said mechanical
operations, second means for detecting characters requiring
printing by said teleprinter, and second delay means operative in
response to said first means and second means when said mechanical
operation is line feed and certain preceding characters did not
require printing, said second delay means inhibiting operation of
said control means for a period of time less than said first
period.
21. A printer for responding to serially received characters
comprising means for responding to a given character, means for
delaying said response to said given character for a first time
interval in response to at least one predetermined character
received prior to said given character, means for delaying said
response to said given character for a second time interval in
response to at least a different one predetermined character
received prior to said given character, and means for delaying said
response to said given character for a time interval different from
said first and second time intervals in response to at least one
predetermined character received after said given character.
22. Means for sensing in a predetermined sequence printable and
nonprintable characters stored in a storage device, means for
reading in said predetermined sequence said sensed characters to
produce electrical signals representative of said sensed
characters, means responsive to the reading of at least one
particular nonprintable character for initiating a given time delay
period, means for sensing and reading in said predetermined
sequence nonprintable characters during said time delay period
until a printable character is sensed, means responsive to said
last-named sensed printable character for delaying further sensing
and reading of characters until said time delay period has expired,
and means for resuming sensing and reading of characters in said
predetermined sequence after said time delay period has
expired.
23. An arrangement according to claim 22 wherein said at least one
nonprintable character comprises a nonprintable character requiring
a greater time period for execution than the longest time period
between printing of two successive printable characters stored in
said storage device.
24. An arrangement according to claim 23 further comprising means
responsive to electrical signals representative of printable
characters for causing printing thereof and responsive to
electrical signals representing nonprintable characters for
executing nonprinting functions.
25. Means for serially sensing printable and nonprintable
characters stored serially in a storage device, means for reading
said sensed characters at a first rate to produce electrical
signals representative of said sensed characters, means responsive
to one particular read nonprintable character for delaying reading
of the next following printable character for a given time period
but not delaying the reading of all nonprintable characters sensed
during said period before said next following printable character,
means responsive to a second particular read nonprintable character
immediately following said first-mentioned particular read
nonprintable character for reading the next following sensed
characters at a second rate as long as such next following sensed
characters are said second particular nonprintable characters.
26. Means for serially sensing printable and nonprintable
characters stored serially in a storage device, means for reading
said sensed characters at a first rate to produce electrical
signals representative of said sensed characters, means responsive
to at least one of several read nonprintable characters for
delaying reading of the next following printable character for a
given time period but not delaying the reading of all nonprintable
characters sensed during said period before said next following
printable character, means responsive to a predetermined one of
said several read nonprintable characters immediately following
said first-mentioned read nonprintable character for reading the
next following sensed characters at a second rate as long as such
next following sensed characters are said predetermined one of said
several nonprintable characters.
27. An arrangement according to claim 26 wherein said several
nonprintable characters comprise a line feed, a carriage return, an
escape and a back space and said predetermined one of said several
nonprintable characters comprises a line feed.
28. Means for serially sensing printable and nonprintable
characters stored serially in a storage device, means for serially
reading said sensed characters to produce electrical signals
representative of said sensed characters, means responsive to at
least one of several read nonprintable characters for delaying
reading of the next following printable character for a given time
period but not delaying the reading of at least one of
predetermined ones of said nonprintable characters sensed during
said period before said next following printable character.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to readers for stored data; more
particularly, it concerns a system that provides automatic control
of a reader and permits both automatic and manual control of the
storage medium editing functions.
The rapidly expanding field of communications relies more and more
upon automatic data-handling equipment. Such equipment must be
capable of accurate and extremely fast transmission and reception
of data. By the elimination of manual operations, it has been found
that not only speed but also reliability can be increased.
Oftentimes, data-handling systems include the use of either
magnetic or punched recording media. The recording medium is run
through reading equipment in order to interpret its contents and
control operation of suitable transmitting or utilization
equipment.
2. Description of the Prior Art
Both magnetic and punched tape recording systems utilize binary
codes to record information. According to such usage, the presence
or absence of a magnetic "bit" or a "hole" is representative of a
logic 1 or logic 0. A large number of code systems have been
developed using discrete permutations of a particular number of
bits to represent specific numeric, alphabetic, and command
characters. The system adopted for a particular use depends upon
the requirements peculiar to that use. It may also be stated that
generally, the selection of magnetic or punched recording media is
also dependent upon the peculiarities of each use. In many cases,
the media are direct equivalents of one another.
At the present time, recorded data is used extensively in
telecommunications, machine tool control, accounting, and
computing. In addition, it is being used with increasing success in
the office equipment field. Teleprinters and typewriters are now
used to convert data from coded tapes to conventional language
texts. On the other hand, data is sometimes transmitted in its
original form to remote locations where it is simply
reproduced.
The great advantages of high-speed operation have resulted in the
development of equipment that responds to data much more rapidly
than can be physically monitored by human operators. Thus, parity
check techniques have been developed which permit automatic testing
for errors and which also provide the means for initiating steps to
remove these errors. Nevertheless, it is still necessary and
desirable to provide means for the override of automatic operation
by a human operator in order to effect editing operations that
cannot be stored for automatic implementation.
Two presently used data-handling systems may be considered in order
to appreciate the types of problems the subject invention is
intended to solve.
The first system involves telecommunication wherein a tape controls
the data presented to a teleprinter from a tape reader. The control
tape may contain too much data, undesired repetitive data, or
erroneous data. The presentation of such data to the teleprinter is
undesirable. Accordingly, means must be provided for detecting its
presence and selectively omitting it. Existing equipment in some
instances offers this capability; however, undue complications and
excessive time are involved in accomplishing the desired functions.
The control tape may also contain original data that is to be
replaced with new data. In this case, means must be provided for
detecting the time of presentation of the original data and then
effecting its replacement. Here too, existing equipment offers
highly unsatisfactory means for accomplishing the desired
functions.
Similar problems occur in the office equipment field wherein
automatically operated typewriters are controlled by tapes
developed during the typing of a draft. In this type of system, the
final copy of a text is developed by permitting the tape to control
the typewriter only when approved passages are being typed. When a
portion of the original draft is to be modified, a human operator
may override the tape control and manually insert new matter.
SUMMARY OF THE INVENTION
The present invention contains a number of features of particular
value in the systems mentioned above. Although the illustrative
embodiment refers to the use of a particular type of punched tape,
it will be apparent that other recording systems can be used, such
as magnetic recording, or systems where signals representing
characters are recorded in a given sequence along a line. For
purposes of description, it has been assumed that the tape reader
is associated with a teleprinter which is responding to the data
that is read. Obviously, this specific combination of equipment is
also not necessarily germane to the invention and other equipment
may be used in conjunction with the novel elements of the tape
reader system and controls.
Since the embodiment of the invention described hereinafter
functions with a teleprinter, the ASCII code system has been
adopted. It is contemplated that a punched tape having nine columns
is employed. Seven of these columns represent bits of a binary
code; the eighth column is the parity check bit; and the ninth
column contains sprocket holes. For purposes of simplicity, when
reference is made to a "character," it will be understood that this
means a printable character such as an alpha-numeric symbol or
nonprintable character such as line feed, which is represented by a
particular permutation of binary indications on the tape. A "word"
is an assembly of printable characters generally set off from the
adjacent text by a nonprintable character such as the code "SP"
(space), or horizontal tab, carriage return or a printable
character such as a period. A "line" is a collection of printable
characters set off at each end by a nonprintable character such as
the code "CR" (carriage return) or a printable character such as a
period, etc. It is important when responding to a tape reader,
particularly with a teleprinter, that the tape reader provide
adequate timing for the various mechanical functions that may be
required by the teleprinter. For example, if the teleprinter is
commanded to backspace, this is a mechanical operation that
requires a discrete time. In order to avoid forwarding characters
to the teleprinter at a time when it cannot respond, the tape
reader must accordingly be delayed for an appropriate interval. The
same situation is true with respect to other commands such as
carriage return and ribbon change.
An object of this invention is to provide an improved arrangement
for reading and editing characters stored along a path in a
recording medium.
An object of the invention is to provide an improved character
reader (i.e., either printable or nonprintable) control system
including means for detecting particular characters prior to the
forwarding thereof to subsequent equipment.
Another object of the invention is to provide an improved character
reader control system including means for automatically initiating
specific reader operations upon detection of particular
characters.
It will be appreciated that some commands, such as line feed,
carriage return, etc., require a longer period of time to execute
than others. In view of this fact, it is desirable to provide
variable delays in accordance with the particular command detected
and furthermore, in accordance with the nature of the next
character or characters. In the past, it has been the practice to
follow commands such as line feed "LF" by a series of nonprintable
characters on the tape in order to provide the necessary time
delay. With the present invention, the tape reader equipment
automatically responds to detection of a line feed code and
consequently, it is not necessary to precode a tape to provide the
necessary time delay.
Another object of the invention is to detect particular commands
such as mechanical commands of line feed, etc., and effect delays
in the transmission of subsequent printable characters until such
commands can be responded to by the receiving equipment.
Yet another object of the invention is to provide for detection of
commands and to provide variable delays in the transmission of
subsequent data depending upon the nature of the subsequent data
and the nature of the command itself.
It is also of value to be able to detect particular characters
other than the aforementioned printer control characters and
initiate special reader operation in response thereto. For example,
a delete ("DEL") character is presented on tape by activating all
possible bits. This character is commonly used to erase an
erroneously entered character or, in some cases, it is used to
provide a time delay for operation of external equipment. It is
advantageous to have the option of skipping such characters if
desired. It may also be desired to skip whole paragraphs in certain
texts. Thus, means for detecting the commands for normal paragraph
indentation and implementing such skipping are of value. Still
further, any such skipping should preferably be carried out at a
high rate of speed.
Another object of the invention is to provide an improved tape
reader control system wherein the detection of certain characters
will automatically initiate high-speed operation of reader until
detection of some other particular character or characters.
When a tape is being read in order to either generate a new tape or
to transmit only selected information thereon, it is extremely
important to be able to stop the printer on particular characters,
words, or lines. This permits selective editing. Since normal
high-speed reading precludes operator intervention, in effecting
this type of editing, it is necessary to determine a target area
for the editing by reading specific portions of the tape at a slow
enough speed to ascertain their content. Subsequent to this
determination, it becomes necessary to provide means for omitting
the desired portions of the tape and/or for possibly inserting
other matter in place thereof.
Another object of the present invention is to provide an improved
character reader control system including means for slowing down
the reader and selectively investigating either the next character,
word, or line prior to forwarding this data to the connected
equipment.
Another object of the invention is to provide an improved character
reader control system having means for selectively and
automatically omitting characters, words, or lines.
A further object of the invention is to effect omission of any
desired portion of the data on the recording medium at a greater
speed than the normal transmission rate.
Modern telecommunications provide means for requesting the
receiving equipment to respond as to whether or not remote parity
checking has established that the received data is accurate. Thus,
the receiving equipment will send to the transmitting station
either a "NAK" (not acknowledged) or an "ACK" (acknowledged) code
if the received data does not satisfy parity requirements, or if it
does satisfy parity requirements, respectively. In response to
these acknowledgement signals, the transmitting station either
repeats the preceding block of data, or proceeds with the
transmission. At the remote location, the receiving unit records
the acknowledgement signal on the tape that is being generated.
Thus, where a block of data is transmitted which does not satisfy
parity requirements, this block of data will appear on the
recording tape followed by "NAK." Where the block of data does
satisfy parity requirements, it will be followed by "ACK." During
the reproduction of the tape, it is, of course, desirable not to
reproduce the portions which are inaccurate as indicated by the
"NAK" symbol. In order to eliminate these portions, the tape may be
run through the reader in a reverse direction and as soon as the
"NAK" symbol is discovered, the portion of the tape between it and
the preceding "ACK" symbol will be deleted.
It is an object of the present invention to provide means for
recognizing "NAK" characters and for subsequently running the
reader at a high speed until an "ACK" character is detected.
Another important factor in the reading of tapes relates to what
would appear to be a very simple matter. This concerns the
detection of the end of the tape. In the past, this detection has
been accomplished by mechanical means.
It is another object of the present invention to provide electronic
means for detecting the end of tape and to thereafter automatically
terminate operation of the equipment.
Another object of the invention is to provide means responsive to
either remote electronic or manual stimulus to reverse the tape
within a reader at any desired time.
Further objects and features of the invention will become apparent
from the following description, which is taken in conjunction with
the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a functional block diagram generally illustrating the
functions carried out by the tape reader and data utilization
device, such as a printer, of the present invention and showing the
relationship between various fundamental functions;
FIGS. 2-9 are individual portions of a logic diagram setting forth
an illustrative embodiment of the invention;
FIG. 2 comprises the elements operative to initiate reader
operation, control generation of reverse stepping pulses, and
respond to teleprinter control during transmission;
FIG. 3 comprises the elements for establishing different delay
conditions in response to line feed commands, and the elements for
detecting the tape-out condition;
FIG. 4A comprises the gates for developing the Advance and Read
signal for the tape reader and the elements responsive to the
synchronizing signal from the teleprinter;
FIG. 4B comprises the elements for initiating and indicating the
READ NEXT, OMIT NEXT, and BACKSPACE modes of tape reader
operation;
FIG. 5 comprises the elements for initiating the selection of
character, word, or line discrimination in the READ NEXT and OMIT
NEXT modes;
FIG. 6 illustrates typical elements for providing the outputs from
each channel of the tape reader to the control system and to the
associated equipment;
FIGS. 7A-7C illustrate several typical decoding circuits responsive
to the characters appearing under the head of the tape reader to
produce control signals;
FIG. 8 comprises the elements for developing forward stepping
pulses for the tape reader, for performing PARITY EDIT operations,
and for performing SKIP DELETES operation; and
FIG. 9 comprises elements operative to permit teleprinter control
over the tape reader in the event that it receives incorrect
data.
DESCRIPTION OF THE PREFERRED EMBODIMENT
General Description
FIG. 1 is presented to illustrate the basic functions that can be
performed by the tape-reading system of the present invention. In
this figure, various functions are denoted by blocks and the
relationship between the blocks is also depicted. It should be
understood that not all of the functions that can be performed by
the equipment appear in FIG. 1. In order to appreciate the full
capability of the system, the reader is directed to the more
detailed circuit description made hereinafter in conjunction with
the logic diagrams of a particular embodiment.
In the illustrated embodiment, use is made of a punched tape reader
that is responsive to pulses to advance or backspace by one step
with each pulse. Each step places the bits representative of a
single character in the reading position. Thus, the character can
be determined and the reader controlled in response thereto. If the
character should not be forwarded to connected equipment, the
control system will make suitable provisions. It has been assumed
that recording tape provides nine output indications. These may be
developed in the conventional manner with photoelectric means which
detect the presence or absence of the punched holes in the tape, as
well as the sprocket holes. The presence or absence of a hole is
indicated on a respective output lead. When a hole is present, the
corresponding output lead provides a signal which will be
considered in the following control logic as being a logic 1
signal.
The tape reader system of the invention can function in four
discrete operating modes. These modes are: RUN, READ NEXT, OMIT
NEXT, and BACKSPACE. Pushbuttons are provided to establish each
mode of operation and the particular circuit functioning will be
described and made clear in connection with the following detailed
description of the invention. FIG. 1 relates generally to the
functions that are performed in the various operating modes.
The Tape Reader 1-10 appears in the upper central portion of FIG.
1. The output of Tape Reader 1-10 which consists of the
aforementioned nine signal leads is applied to a Decoder 1-23 and
Data Gate 1-24. Decoder 1-23 produces binary signals on individual
leads. These signals are employed by the control system to initiate
and terminate the various operations of the tape reader. The
decoder monitors each character as it appears in the reading
position on the tape reader.
When it is desired to start operations, Run/Stop circuitry 1-13 is
activated and provides a start impulse via Reader Controls 1-12 to
Tape Reader 1-10. When this occurs, the Reader will read the
character appearing in the read position and advance one step. A
Teleprinter 1-11 is illustrated in conjunction with the reader
control system. The Teleprinter 1-11 is responsive to the
information presented thereto via Data Gates 1-24 and after it has
completely digested the information, it returns a synchronizing
signal to Advance And Read Gates 1-25 which indicates to the Tape
Reader control system that a further reading cycle should be
initiated. It should be noted that the first operation of the tape
reader requires a start impulse from Run/Stop circuitry 1-13.
Thereafter, the Teleprinter, or similar equipment, produces the
necessary synchronizing signals for continuously advancing the Tape
Reader.
In most situations, the synchronizing signals from Teleprinter 1-11
will successively initiate the reading cycles. However, special
Delay means 1-27 and 1-28 are provided for delaying the
synchronizing signal when a preceding character has commanded
teleprinter mechanical operations. For example, these delay means
operate when the commands call for a backspace, carriage return, a
change in ribbon color, or a line feed. As a general rule,
following any of these four commands, Decoder 1-23 activates a Long
Delay circuit 1-27 which inhibits operation of Advance And Read
Gates 1-25 for the amount of time required to effect the called-for
mechanical action of the Teleprinter 1-11. After this time has
elapsed, the previously received synchronizing signal from
Teleprinter 1-11 is effective via Gates 1-25 to generate the
Advance And Read signal.
It will be appreciated that sometimes the character following the
line feed command will not be a printable character such as a bell,
or a second line feed command. Where this is the case, it is not
necessary to delay the reading of this character because the
character will not require the teleprinter to effect a printing
operation. Accordingly, the Decoder 1-23 determines whether or not
the succeeding character is a printable character. In the ASCII
code system, printable characters have either bit-6, or bit-7, or
both bits present in their code. Thus, the presence of either of
these bits can be easily detected. If a printable character does
not occur following an LF, the next line feed or non-printable
character command causes Short Delay 1-28 to inhibit the generation
of the next Advance And Read signal in response to the
synchronizing pulse from Teleprinter 1-11. Thus, it is seen that in
order to completely minimize the delays required by line feed,
carriage return, etc., two distinct delay circuits are provided in
the present invention.
In connection with the editing aspects of the invention, attention
is directed to the left-hand portion of FIG. 1. The control system
makes it possible to review the data on the tape before it is
forwarded to subsequent equipment. In most instances this
capability is used in conjunction with the high speed omission
features of the invention. However, with minor modifications, this
capability can also be utilized in conjunction with data addition
means.
When it is desired to read the information appearing on the tape in
order to perform possible editing operation, Read Next circuitry
1-16 is activated. Following this, the operator selects circuitry
1-17, 1-18, or 1-19, depending upon whether it is the next
"Character, Word" or "Line," which is of interest. When the
selection is made, the equipment automatically functions to slow
down and read only the desired next character, word, or line.
Assuming that it is the next character which is of interest, the
Character Selection circuitry 1-17 initiates start of the Reader
via Advance And Read Gates 1-25 and Reader Controls 1-12. The Tape
Reader 1-10 operates to advance and read the next character. As
soon as Decoder 1-23 detects a sprocket signal, Comparator means
1-20 is activated to stop the Reader so that only one character
will be read. A similar arrangement is provided for reading the
next word or line. The distinction in operation comes about as a
result of having to stop Tape Reader 1-10 upon detection of
something other than sprocket holes. Thus, when one wishes to read
the next word, a start Reader signal is generated and the Reader
1-10 will continue operation in response to synchronizing signals
until the Decoder 1-23 detects the presence of a character denoting
the end of a word. Some of these characters are "space,"
"horizontal tab," "carriage return," and "line feed." On the other
hand, when one is interested in reading the entire next line, the
Comparison means 1-19 will permit operation of the Tape Reader 1-10
until a carriage return or line feed signal is detected by Decoder
1-23.
Having selectively moved the Tape Reader 1-10 in order to consider
the character, word, or line presented thereby, it becomes possible
to effect automatic omission of these characters rather than
forwarding them to connected equipment. When it is desired to omit
a character, word, or line, Omit Next circuit 1-15 is activated. In
this operating mode, the Character, Word, or Line circuitry 1-17,
1-18, 1-19, is effective to function until appropriate codes are
detected by the Decoder and used to terminate the particular
function being performed. A specific unique feature of the
invention relates to the provision of Rapid Advance means 1-26
which is operative in the event of Omit Next operation. With Rapid
Advance means 1-26, rapid advance signals are applied to Tape
Reader 1-10 during omission of data so that is is not necessary to
await the usual slower occurring synchronizing signals from
Teleprinter 1-11, In this way, a minimum amount of time is lost and
high-speed handling of the data is effected.
This high-speed operation is also called into play when Parity Edit
or Skipping Functions are being performed.
In order to understand the functioning of the Parity Edit features
of the invention, it will be recalled that when tape is initially
prepared, it is common to insert the characters "NAK" and "ACK" at
the end of blocks of data in accordance with whether or not the
preceding material satisfies parity conditions. When using the
Parity Edit feature of the invention, the tape is inserted in a
reverse direction and the Reader 1-10 is started. When the Decoder
1-23 reads a "NAK" character, the Parity Edit circuitry 1-29
immediately enables Rapid Advance means 1-26 and the tape advances
at a rapid rate without the reading of data until and "ACK" signal
is detected by Decoder 1-23. At this time, the Reader 1-10 is
slowed to its normal operating speed and goes through the normal
reading cycles in response to each synchronizing signal
received.
The high-speed operation of the Tape Reader, without forwarding
data to other equipment, is also advantageous in implementing the
skipping of undesired portions of data. Such skipping is
implemented by Skip circuitry 1-31 which is enabled when a
character is detected by Decoder 1-23 that signals the start of
such undesired portions. The following logic schematics illustrate
the use of this skipping feature to skip delete characters. This is
of particular value since such characters are generally entered on
the tape simply to obliterate errors or create time delays, not
required in the advanced equipment contemplated herein. On the
other hand, the skipping circuitry can also be activated by
indented material, tables of figures, and any other desired
material that can be detected by the presence of distinctive
characters.
CIRCUIT SYMBOLOGY
The logic diagrams of FIGS. 2 through 9 are composed primarily of
flip-flops and NOR logic gates. For convenience in understanding
the functions of the various components, the flip-flops are
designated with a two-part designation. In this designation, the
numerical prefix represents the figure in which the element appears
and the alphabetical suffix is generally a word or acronym
descriptive of function performed by the flip-flop. For example,
flip-flop 2-RUN appears in the left central portion of FIG. 2 and
is placed in a "set" state in order to initiate the RUN operating
mode. Similarly, flip-flop 2-SRV appears in FIG. 2 and is placed in
a "set" state to Start Reverse operation of the Reader. The leads
and other elements also bear numerical prefixes indicative of the
figure in which they originate; however, numerical suffixes are
used in order to differentiate between the various elements in each
figure.
As a further aid in understanding circuit operation and recognizing
the leads over which important control signals are applied,
functional lead descriptions are sometimes used in addition to the
numerical designations. These functional descriptions are
associated with the appropriate leads by means of small arrows. For
example, lead 9-18 on the left edge of FIG. 2 is designated
"Trigger Start Reverse." This indicates that the signal for
triggering the start of reader reverse drive is transmitted by this
lead. The bar placed over this functional lead description
indicates that the operative signal is a logic 0. The absence of
such a bar indicates that the operative signal is a logic 1.
The NOR logic gates used in the circuitry are of conventional
design. The logic function NOR in Boolean Algebra is well known and
can be defined as follows for a two input gate: If one or both
inputs have a logic 1 applied thereto, the output will assume a
logic 0 state. Stated another way, if neither one input nor the
other input has a logic 1 applied thereto, the output will assume a
logic 1 state. Two types of symbols have been used for illustrating
the NOR gates. One of these symbols (e.g., see gate 2-16 on the
left of FIG. 2) has small circles on the input leads. This symbol
is used where the desired operative output is a logic 1. The other
symbol (e.g., see gate 2-20 on the left of FIG. 2) has a small
circle on the output lead. This symbol is used where the desired
operative output is a logic 0. Although the symbols are different,
the gates may be physically the same and they both perform the same
NOR operation.
The standard flip-flop used in the circuit diagram has five input
terminals and two output terminals. The specific function of each
terminal has been included in the illustration of typical flip-flop
2-R, appearing in the center of FIG. 2. The application of logic 1
to the set input will place the flip-flop in a "set" state. The
application of a logic 1 to the reset input will place the
flip-flop in a "reset" state. When "set" the flip-flop provides a
logic 1 at its set output and a logic 0 at its reset output. The
reverse is true of the "reset" state.
Generally, a flip-flop is operated by the application of trigger
pulses to the trigger input. A trigger pulse is one which goes to a
logic 1 condition. Frequently these pulses are provided in a
uniform train from a clock pulse generator. In response to a
trigger pulse, a flip-flop assumes the state dictated by the
signals on its set steering and reset steering inputs. The
application of a logic 0 to either steering lead will be effective
to switch the flip-flop so that the corresponding output provides a
logic 1 upon occurrence of the trigger pulse. If the corresponding
output of the flip-flop is already at logic 1, no change of state
will occur. It will be noted that the steering leads have small
circles thereon. This is consistent with the previously noted
convention that such circles indicate that the operative signals
applied to these leads must be logic 0. Often, the steering leads
are shown connected to a circle enclosing a negative sign, or to a
"ground" symbol. The former connection denotes a logic 1 source,
and the latter, a logic 0 source.
In keeping with other symbol conventions, the output leads of the
flip-flop can be identified by the source. Thus, the lead
associated with the set output of flip-flop 2-R may be designated
2-R and the lead associated with the reset output may be designated
2-R.
Consideration will now be given to the detailed logic schematic
drawings set forth in FIGS. 2 through 9. Since the illustrative
embodiment of the control system is described in conjunction with a
tape reader interconnected to a teleprinter, the tape reader and
teleprinter are represented by dashed line boxes at the top of FIG.
2. Each box shows the pertinent input and output signals associated
with typical equipment of this type.
RUN MODE OF OPERATION
Since the teleprinter provides synchronizing signals for the
initiation of tape reading cycles, it is necessary to provide a
start read pulse only at the at the beginning of the RUN operating
mode. Thereafter, the tape reader will receive through the control
system, FORWARD STEP signals that are initiated by the teleprinter.
On the drawings, the synchronizing signal is labeled RNC (Read Next
Character).
Assuming that power has been supplied, the tape reader system is
placed in a RUN mode by depressing the Run/Stop button appearing at
the upper left corner of FIG. 2. This removes the logic 1 from the
set-steering input of flip-flop 2-RU1. Accordingly, on occurrence
of the next CP1 clock pulse from Clock Pulse Generator 2-CPGI,
flip-flop 2RU1 assumes a set condition and a logic 0 appears at the
reset output thereof. This logic 0 is applied over lead 2-10 to the
set-steering input of flip-flop 2-RU2. Thus, upon the next
appearing CP1 clock pulse, flip-flop 2-RU2 assumes a set state and
provides a logic 1 at its set output. The latter signal is applied
via diode 2-11 as a trigger pulse to the Run flip-flop 2-RUN which
is connected to be self-steering, i.e., its set output and reset
output are interconnected to the set-steering and reset-steering
steering leads, respectively. Accordingly, the effect of the logic
1 signal applied via diode 2-11 is to always switch the state of
flip-flop 2-RUN. The state of flip-flop 2-RUN indicates whether or
not the equipment is to either begin operation or cease
operation.
Flip-flops 2-RU1 and 2-RU2 are provided simply in order to prevent
any momentary switch contact bounce of the Run/Stop pushbutton from
effecting the repetitive operation of flip-flop 2-RUN. Obviously,
other means could be provided for effecting this operation. As soon
as the pushbutton is released, it connects a logic 1 to the reset
terminals of both flip-flops and they return to the reset
condition.
Clock Pulse Generator 2-CPGI provides synchronizing pulses for the
entire control system. In the particular implementation of the
invention described hereinafter, the signal provided by the clock
pulse generator was a 20 microsecond logic 1 pulse that was applied
at a repetition rate of approximately 120 per second.
The four operating modes of the control system are controlled by
the condition of Run flip-flop 2-RUN, Read Next flip-flop 4-RN,
Omit Next flip-flop 4-ON, and the Backspace flip-flop 4-BS.
Circuitry is provided, as described subsequently in connection with
FIG. 4, to initially place each of the four flip-flops in the reset
condition. During subsequent operation of the circuitry, only one
of these flip-flops will be permitted to remain in a set condition
at any time. Thus the flip-flop that is set will establish the mode
in which the circuit is operating.
Having set Run flip-flop 2-RUN, it is necessary to generate the
start pulse for presentation to the tape reader so that the first
read cycle may begin. This start pulse is generated by the Start
Reader flip-flop 2-SR appearing in the lower left quadrant of FIG.
2. When Run flip-flop 2-RUN is set, a logic 1 triggering pulse is
delivered over lead 2-12 to the trigger input of Ran flip-flop
2-RA. The set-steering input of Ran flip-flop 2-RA has a logic 0
provided thereto; thus, upon appearance of the trigger pulse,
flip-flop 2-RA switches to a set state. The switching of flip-flop
2-RA is effective via NOR gate 2-13 to apply a logic 0 to the
set-steering input of Start Reader flip-flop 2-SR. Since the Start
Reader flip-flop is thereby steered to a set condition, the next
triggering impulse applied thereto from Clock Pulse Generator 2-CPG
II, will set it.
Clock Pulse Generator 2-CPG II provides a signal that assumes a
logic 1 state at intervals of 12 microseconds and has a duration of
approximately 1.5 microseconds. Obviously, both clock pulse
generators can be designed in any suitable fashion.
The setting of Start Reader flip-flop 2-SR, supplies a logic 1
signal via lead 2-14 to the reset terminal of flip-flop 2-RA, and
consequently places it in a reset condition. The reset output of
flip-flop 2-SR is connected to its reset-steering input. Thus, upon
the next occurring 2-CP2 clock pulse the Start Reader flip-flop
itself will be reset. Thus, during its set condition, the set
output of flip-flop 2-SR provides a 12 microsecond wide logic 1
signal.
Reference is made to FIG. 8. The logic 1 generated at the set
output of Start Reader flip-flop 2-SR, is applied via NOR gates
8-10, 8-11, and 8-12 to the set-steering input of the Step
flip-flop 8-STEP appearing at the center of FIG. 8. As a result of
the inversions in each of the NOR gates, this set-steering signal
is of the appropriate logic 0 state. Thus, upon occurrence of the
next CP2 clock pulse on the trigger input of step flip-flop 8-STEP,
this flip-flop will be set. The setting of flip-flop 8-step is
effective through gates 8-13, 8-14, 8-15, and 8-16 to provide a
very narrow Forward Step pulse at the output of NOR gate 8-16. The
development of this pulse includes the use of the differentiating
circuit 8-18 connected between gates 8-14 and 8-15. The pulse is
applied to the tape reader and will cause the tape to be advanced
by one character. As mentioned previously, this is the only start
pulse that needs to be generated by the control system. All
subsequent synchronizing pulses will be supplied by the teleprinter
when it is ready to receive the next character.
It will be noted that a number of additional inputs are illustrated
for the various gates thus far encountered. Where necessary, the
application of signals to these inputs will be described in detail
hereinafter. Where the specific mention of these inputs is not
made, the source of the signals is made obvious by the lead
designations. An understanding of circuit operation in response to
such signals will be possible since the functioning of the circuit
elements is easily appreciated. It is believed that the specific
recitation of the signal paths followed and the component operation
in response to each signal, would unnecessarily burden the
discussion of this illustrative embodiment of the invention.
READER SIGNAL HANDLING AND DECODING
Having noted the manner in which the Forward Step signal is
generated and presented to the Tape Reader, it is worthwhile to
consider the nature and handling of outputs from the Tape Reader.
For this purpose, attention is directed to FIG. 6. The circuits
illustrated in FIG. 6 represent the nine outputs from the Tape
Reader. Circuits 1 through 7 provide the 7 coded bits of each
character and circuit 8 provides the parity check bit. The ninth
circuit provides the sprocket signal. The first seven channels from
the Tape Reader are applied to transistors 6-11 through 6-17. The
outputs of the transistors are applied to a series of gates 6-21
through 6-27 which inhibit transfer of information to the
teleprinter or similar equipment until an enabling signal 8-STEP is
provided. This enabling signal is generated at the reset output of
Step flip-flop 8-STEP when the flip-flop is in a set state.
The equipment is designed to read the character resting in the
reader first, and then advance the tape by one step to the next
character position. In order to assure a correct signal being
transferred to the teleprinter, it is necessary to provide a strobe
pulse which will be delayed sufficiently after the 8-STEP pulse has
opened the gates. This strobe is provided to the teleprinter by a
Reader Strobe flip-flop 8-RS appearing in the upper central portion
of FIG. 8. The setting of Step flip-flop 8-STEP provides the
necessary logic 0 steering signal to Reader Strobe flip-flop 8-RS.
Consequently, upon occurrence of the next CP2 triggering signal,
Reader Strobe flip-flop 8-RS is set and provides a logic 1 output
at its set terminal. This Reader Strobe signal is supplied to the
Teleprinter to indicate that the data presented from the Tape
Reader may be accepted. Upon receipt of all information from the
Reader, the teleprinter in any known manner will return a signal
labeled Strobe In. The Strobe In signal is supplied to the reset
terminals of the Step and Reader Strobe flip-flops 8-STEP and 8-RS
in order to reset them. At a somewhat later time, after the
teleprinter has digested and completed its read-in functions, it
will provide the necessary RNC synchronizing signal to reinitiate
the read and advance cycle previously described.
Before proceeding with a description of the circuit operating
during normal response to the various possible commands, reference
is made to FIGS. 7A through 7C. These figures illustrate typical
decoding circuits which operate to provide discrete signals in
accordance with the detection of certain important characters in
the reading position at the TAPE Reader. Referring to FIG. 7A, it
will be seen that there are seven diodes. The input to each of
these diodes is designated by a number from 1 to 7 which is either
barred or plain. These input indications represent the signal bit
of the various channels on the tape for a particular character.
Recalling that we have assumed use of the ASCII code system, it
will be seen that a discrete output is provided from this
particular decoding circuit when a logic 1 appears at the terminal
labeled "sprocket," and with the character 1111111 appearing on the
tape. This is the delete character in which all possible holes are
punched. Under this condition a logic 1 signal will be provided on
the lead marked "DEL" and a logic 0 will be provided on the lead
marked "DEL."
Other typical decoding circuits are shown in FIG. 7B and FIG. 7C.
In the case of FIG. 7B, when the character that is read has the
binary code 0101000, a logic 1 will appear on the lead labeled
"LF." This indicates that the character is a Line Feed command in
accordance with the ASCII code designations. Similarly, when the
character is 0110000, a logic 1 will appear on the "ACK" lead. This
indicates that an acknowledgement signal has been obtained from
monitoring equipment and that the previously printed data block
satisfies all parity conditions. Similar decoding gates are
provided for developing positive signals for any particular
character that will be used in conjunction with the initiation or
implementation of operations by the tape reader control system.
READER DELAY OPERATIONS
As previously mentioned, depending upon the character stored in the
tape, various actions must be taken by the control circuitry. For
example, it is necessary to halt the flow of characters from the
Tape Reader to the Teleprinter, momentarily after delivering a
"Carriage Return" signal code, in order to permit the mechanical
carriage return action to be carried out. The delay is effected by
preventing immediate response to the synchronizing RNC pulse from
the Teleprinter and thereby delaying the generation of the Forward
Step pulse that is normally supplied to the Reader. The Read Next
Character flip-flop 4-RNCS appearing in the upper portion of FIG.
4A, in cooperation with gates 4-12 through 4-21 provide modifying
circuitry which will either permit immediate response to the
synchronizing pulse or delay the response.
In the lower right quadrant of FIG. 3, there is a timing circuit
made up of resistor and capacitor-timing elements and gates 3-10
and 3-11. This timing circuit is activated by the output of gate
4-14 in FIG. 4 and the output of gate 3-12 in the left center
portion of FIG. 3. Long delay flip-flops 3-LD1, 3-LD2, and 3-LD3
function in cooperation with the timing circuit.
In essence, gate 4-14 operates to provide a logic 0 whenever the
Decoding circuitry detects a change ribbon ("ECS"), a backspace
("BS"), or a carriage return ("CR") code. This is illustrated on
the drawings by the logic notation ESC+BS+CR. The logic 0 signal is
applied to the set-steering lead of long Delay flip-flop 3-LD1. The
RNC synchronizing pulse from the Teleprinter is applied as the
trigger to this flip-flop; accordingly, when the RNC pulse is
provided, it will set flip-flop 3-LD1. The logic 1 appearing at the
output of flip-flop 3-LD1 is applied via gate 3-12 to the
set-steering input of flip-flop 3-LD2. Upon occurrence of the next
CP2 clock pulse, flip-flop 3-LD2 will be set. The resulting logic 0
signal at the reset output of flip-flop 3-LD2 is applied to the
set-steering lead of flip-flop 3-LD3, and upon occurrence of the
next CP1 clock pulse, flip-flop 3-LD3 is set.
The setting of flip-flop 3-LD3 provides a logic 1 signal which
resets flip-flop 3-LD1 via lead 3-13. This signal is also applied
to the reset input of 3-LD2 via lead 3-14. The resetting of the
latter mentioned flip-flop removes the set-steering from flip-flop
3-LD3. The reset output of flip-flop 3-LD3 is connected to its
reset-steering input and it is therefore reset upon appearance of
the next CP1 clock pulse.
While it is set, the logic 1 appearing at the set output of
flip-flop 3-LD3 is applied to one input of the gate 3-11. This
forces the output of gate 3-11 to go to a logic 0 for the period of
the triggering of clock signal CP1. The logic 0 signal is applied
to capacitor 3-15 in order to discharge it and reset the timer in
the event that it was previously in the middle of a timing cycle.
At the same time, the logic 0 output on the reset output of 3-LD3
discharges capacitor 3-16.
When the next appearing CP1 clock pulse resets flip-flop 3-LD3 the
negative going output on the reset output lead is differentiated by
capacitor 3-16 and resistor 3-17 and applied to one input of gate
3-10. This forces the output of gate 3-10 to logic 0 and this is
applied to one input of gate 3-11. Since the reset of flip-flop
3-LD3 places a logic 0 on the other input, gate 3-11 provides a
logic 1 signal on lead 3-40. This marks the beginning of the timing
cycle. The logic 1 signal is applied via a timing circuit
comprising capacitor 3-15 and adjustable resistor 3-19 to an input
of gate 3-10. This closed loop arrangement maintains a logic 1 at
the output of gate 3-11 for the duration of the time interval set
by the adjustable resistor 3-19.
Reconsidering again the instant of time at which flip-flop 3-LD3 is
set, it will be noted that the set output thereof is applied to
gate 4-12 in FIG. 4A. This lead will be at logic 1 and accordingly
a logic 0 output will be provided from gate 4-12 to one of the
inputs of gate 4-15. The other input of gate 4-15 is the 3-LD
signal from the output of gate 3-11. It will be recalled that at
this time, the 3-LD signal is in a logic 0 state as a result of the
resetting of the timer which occurs upon setting flip-flop 3-LD3.
Thus, a logic 1 is presented at the output of gate 4-15 and is
applied to gate 4-20 which in turn presents a logic 0 to an input
of gate 4-21. As will be explained hereinafter, the Omit Next
signal 4-ON and the Start Up Reset signal will both be at logic 0
at this time. Therefore, the logic 0 output from gate 4-20 will
result in the generation of logic 1 at the output of gate 4-21.
This is the Advance And Read signal that is applied to gate 8-10 to
develop a Forward Step signal for the Tape Reader. In response
thereto, the Reader forwards the "ESC," "BS," or "CR" command
character to the Teleprinter. It is now necessary to determine
whether or not the succeeding character on the tape is a printable
character. If so, the control system will have to delay the Reader
operation in response to the next RNC synchronizing signal.
The RNC pulse is received from the Teleprinter at the trigger input
of Read Next Character flip-flop 4-RNCS. This flip-flop is
permanently steered so that upon receipt of the RNC synchronizing
signal, it will be set. As illustrated in the figure, the reset
input of flip-flop 4-RNCS receives the Strobe In signal from the
Teleprinter. It is this signal that indicates the Teleprinter has
completed all action in response to the preceding character. Thus,
flip-flop 4-RNCS is automatically set in response to the RNC signal
and reset in response to the Strobe In signal.
Gates 4-10 and 4-11 function to determine whether or not a
character is printable. Since printable characters in the ASCII
code system have either bit-6, bit-7, or both present in their
codes, gate 4-10 has input signals from channels 6 and 7 of the
reader. The operation of gate 4-10 results in the presentation of a
logic 0 output when either bit-6 or 7 is a logic 1. The only time
this logic 0 output is ambiguous is when the character is delete.
In order to eliminate this ambiguity, the Decoder provides the
"DEL" signal as one input of gate 4-11. Thus, the output of gate
4-11 will only be at logic 1 when there is a printable character
that is not a Delete, and an RNC signal has previously set
flip-flop 4-RNCS. The logic 1 output from gate 4-11 is used to
drive the trigger input of Printable Character flip-flop 4-PC. The
reset steering input of flip-flop 4-PC is permanently held at logic
1 whereas the set steering input is provided with a signal that
will be at logic 0 when the character being read is not a space
("SP"). Thus, flip-flop 4-PC is set when there is a printable
character resting in the read position of the Tape Reader.
When the timing circuit comprising elements 3-15 and 3-19, in the
lower right portion of FIG. 3, has timed out, signal 3-LD at the
output of gate 3-11 will assume a logic 0 state. This logic 0 is
applied to one input of gate 4-18. The other input of gate 4-18 is
connected to the reset output of Printable Character flip-flop
4-PC. Accordingly, if flip-flop 4-PC is in a set condition
indicating that a printable character is ready to be read and that
the RNC-synchronizing pulse has been received, the flip-flop will
provide a logic 0 to the second input of gate 4-18. The output of
this gate then goes to logic 1 and the application of the logic 1
signal through gates 4-20 and 4-21 results in the generation of a
logic 1 Advance And Read signal.
It will be recalled that the time delay operation just described in
response to the detection of a Carriage Return ("CR") signal by the
decoder circuitry. A similar delay is required in the event of a
command for either Backspace or Ribbon Change. Where these
characters are detected, logic 1 signals are applied to gate 4-14
and this is effective to initiate the timing cycle just
described.
Somewhat different considerations are applicable in the event that
the character Line Feed ("LF") is detected. In this case, it is
necessary to delay reading of any subsequent printable character;
however, as previously mentioned, the delay need not be as long as
the one previously described, if the character or characters
between the first and second line feeds are not printable
characters. Thus, if a printable character follows the "LF"
character, it is necessary to start the longer timer just
described. On the other hand, if a nonprintable character (e.g.,
another "LF") follows the "LF" character, a shorter timer may be
initiated, thereby permitting the Teleprinter to rapidly make
repeated Line Feeds.
The signal on the set output of flip-flop 4-PC is applied to the
set input of flip-flop 3-PCLF in the right center portion of FIG.
3. The reset-steering input of flip-flop 3-PCLF is at a logic 0
when a Line Feed character is detected by the Decoder. Thus,
flip-flop 3-PCLF is set if there has been a printable character
detected since the last Line Feed command, otherwise it is reset.
Flip-flop 3-CLF has its set-steering input at logic 0 when there is
a Line Feed character in the printer. This flip-flop is triggered
by the set output of the Read Next character flip-flop 4-RNCS.
Thus, when the character is a Line Feed character, upon occurrence
of an RNC signal from the Teleprinter, flip-flop 3-CLF will be set.
When both flip-flop 3-PCLF and flip-flop 3-CLF are set, a logic 1
is presented at the output of gate 3-27 which is effective via gate
3-12 to set steer Long Delay flip-flop 3-LD2. The next occurring
CP2 clock pulse sets flip-flop 3-LD2 and thereby initiates
operation of the Long Delay Timer as previously described.
If no printable character has been detected since the last Line
Feed command, it is desired that a shorter time be taken prior to
reading of the next character. The shorter timing is effected by
the timing circuit shown in the upper portion of FIG. 3. The timer
consists of flip-flops 3-SD1 and 3-SD2, and includes timing
circuitry comprising capacitor 3-25 and adjustable resistor
3-26.
The conditions for setting the Short Time Delay are established by
connecting the reset output of flip-flop 3-CLF and the set output
of flip-flop 3-PCLF to the inputs of gate 3-20. When both inputs of
gate 3-20 are at logic 0, it supplies a logic 1 trigger pulse to
flip-flop 3-SD1. The permanent set steering of this flip-flop
causes it to set in response to the trigger pulse, and this in turn
set steers flip-flop 3-SD2. Flip-flop 3-SD2 is set by the next
occurring CP2 clock pulse. The setting of flip-flop 3-SD2 produces
a logic 0 at the output of gate 3-24 which is effective to
initially reset the timing circuit comprising capacitor 3-25 and
adjustable resistor 3-26. As was the case of flip-flop 3-LD3,
flip-flop 3-SD2 is self-steered to reset and therefore resets upon
occurrence of the next CP2 pulse. This starts the timing cycle. In
a reset condition, flip-flop 3-SD2 set steers flip-flop 3-SD3 and
when the timing cycle has been completed flip-flop 3-SD3 will be
triggered to the set state and produce a logic 1 signal at its set
output. The logic 1 signal at the set output of flip-flop 3-SD3 is
applied to gate 4-12 in the same manner that the output of
flip-flop 3-LD3 was applied thereto. As a result, an Advance And
Read signal will be produced via gates 4-12, 4-15, 4-20, and 4-21
after the shortened time has elapsed.
In the event that the longer delay timer is activated prior to
initiation of the shorter delay, the longer timer will override the
shorter timer as a result of the action of the 3-LD input to gate
4-15.
All other nonprinting characters that may appear in the tape being
read are effective without delay to generate Advance And Read
pulses at the output of gate 4-21. The circuitry for implementing
this generation of pulses includes gates 4-13, 4-16, 4-19, 4-20,
and 4-21. If the character is nonprintable and not "LF," gate 4-13
provides a logic 1 to gate 4-16. Gate 4-16 produces a logic 0
output when the character is either a Delete or nonprintable or
"LF." Recall that gate 4-14 produces a logic 1 only if the
character is not "ESC," "BS," or "CR." This being true, inverting
the output of gate 4-14 with gate 4-17 provides a logic 0 when the
character does not require a Change Ribbon, Backspace, or Carriage
Return. The outputs of gates 4-16 and 4-17 are applied along with
the reset output of flip-flop 4-RNCS to gate 4-19 and will generate
a logic 1 output therefrom when nonprinting characters other than
the three specified, are read. This output will produce the Advance
And Read signal via gates 4-20 and 4-21.
TAPE OUT CONDITION
It is desirable to stop the Tape Reader when it runs out of tape.
Preferably this should be done electronically and not by a
mechanical sensing means. In accordance with the present invention
this condition is sensed by noting that repeated forward or reverse
step pulses are applied to the Tape Reader without receiving the
corresponding sprocket hole signals which are normally produced
when the sprocket hole sensor sees paper and holes alternately.
The impulses commanding forward or reverse steps are not only sent
to the Tape Reader, they are also applied via gates 3-31 and 3-32
to the trigger input of Step flip-flop 3-ST appearing in the lower
left quadrant of FIG. 3. Flip-flops 3-ST and 3-TO are connected as
a two-stage binary counter. When a tape is in place, the step
impulses will register a count and the sprocket signal will reset
the counter. The resetting is effected through a plurality of gates
3-33 through 3-37. Gates 3-33, 3-34, and 3-35 insure that the
equipment is in one of its operating modes. Gate 3-36 provides a
logic 0 output if the equipment is in one of the operating modes, a
Startup Reset signal is applied, or there is a sprocket signal. A
count of two will result in the setting of Tape Out flip-flop 3-TO.
When this occurs the set output of flip-flop 3-TO is effective via
gates 4-22 through 4-25 in FIG. 4B to reset flip-flops 2-RUN, 4-RN,
4-ON and 4-BS. In other words, the control system is placed in a
stop mode.
READ NEXT OPERATION
Thus far, the circuit operation in response to general operating
conditions following a start impulse has been described. Attention
will now be directed to the specific editing functions which the
present reader control system is capable of performing. The first
of these functions involves the controlled slowing of the Reader in
order to determine the next character, word, or line. This is an
essential operation preparatory to either accepting the information
that is to be presented or modifying it in order to correct it. At
the bottom of FIG. 4B three flip-flops are illustrated. These
flip-flops control the operating modes: Read Next, Omit Next, and
Backspace, respectively.
The Read Next operation is initiated by closure of the Read Next
pushbutton appearing in the lower left corner of FIG. 4B. This
supplies a logic 1 signal to the set input of Read Next flip-flop
4-RN, placing it in a set state. The logic 1 1 signal applied to
the set terminal of flip-flop 4-RN upon depression of the Read Next
pushbutton is also applied via diode 4-28 and lead 4-30 to the
trigger input of flip-flop 4-ON and 4-BS. The result of this
application to the latter flip-flops guarantees that they are
switched to a reset state in the event that they were previously
set. It will be noted that the set-steering input of each of the
flip-flops is permanently at logic 1, whereas the reset-steering
terminals are permanently at logic 0.
If it is desired to read only the next character on the tape, and
then stop the reader, this is accomplished by depressing the
character pushbutton appearing in FIG. 5. The set-steering inputs
of each of the flip-flops 5-CHAR, 5-WORD, and 5-LINE are all
connected to the output of gate 5-13. The inputs to this gate are
the 4-RN signal and the 4-ON signal generated at the set output of
the corresponding flip-flop in FIG. 4. Thus, when either the Read
Next or Omit Next flip-flops are energized, a logic 1 will be
presented to the input of gate 4-13 and the output thereof will be
logic 0, thereby set steering the associated flip-flops. Thus,
operation of the character pushbutton applies a trigger pulse to
flip-flop 5-CHAR and it is set. The consequent logic 1 signal
appearing at the set output of flip-flop 5-CHAR causes a logic 0
signal to be produced at the output of gate 5-14. The inversion in
connected gate 5-15 supplied a trigger pulse to flip-flop 5-OMIT
appearing on the extreme right of FIG. 5. Flip-flop 5-OMIT is
permanently steered to a set condition Accordingly, when it is set,
a logic 0 is produced at its reset output and in the absence of an
Omit Next signal (4-ON), a logic 1 CWL start signal will be
provided at the output of attached gate 5-16. This latter signal
derives its name from the acronym for "Character-Word-Line" start
operation.
Referring to FIG. 2, it will be seen that the CWL start signal is
applied via gate 2-13 to the set steering lead of the Start Reader
flip-flop 2-SR. Consequently, upon appearance of the next trigger
impulse CP2, a Start Reader signal will be provided at the set
output of flip-flop 2-SR and the read cycle previously described
will take place.
Flip-flop 5-OMIT has the tape out reset signal appearing on lead
3-38 applied as a reset input thereto. It will be recalled that
these tape out reset signals are generally developed by the
sprocket holes as the tape is read, and appear at the output of
gate 3-37 in the lower portion of FIG. 3. After the tape has
advanced one character position, flip-flop 5-OMIT is therefore
reset. The state of flip-flops 5-CWLR and 5-OMIT are compared at
gate 8-17 in the left portion of FIG. 8. When flip-flop 5-OMIT is
reset, gate 8-17 provides a logic 1 which resets Stop Strobe
flip-flop 8-SS. The resetting of flip-flop 8-SS blocks the incoming
Advance And Read signal that is being applied via gates 8-10, 8-11,
and 8-12 to the set-steering input of Step flip-flop 8-STEP and
thereby prevents generation of the Forward Step Signal. This
blocking action is effected by the application of the logic 0 from
the set output of 8-SS to one input of gate 8-19. In order to
generate the Forward Step impulse it is essential that one of the
inputs to gate 8-19 be in a logic 1 state. The other input at this
time is at logic 0 state because Run flip-flop 2-RUN is in a reset
state. The logic 0 from flip-flop 8-SS makes the output of gate
8-19 a logic 1 and this prevents the set steering of flip-flop
8-STEP. The blocking action is very fast and will occur before the
operator removes his finger from the character pushbutton. When the
button is released its back contacts apply a trigger pulse to
flip-flop 5-CWLR via gates 5-11 and 5-12. The setting of flip-flop
5-CWLR results in the application of a logic 1 signal to the reset
inputs of each of the Character, Word, and Line flip-flops placing
them in a reset condition.
In recapitulation it will be seen that, as a result of depressing
the Read pushbutton and the Character pushbutton, a single Forward
Step signal activated the Reader and the subsequently developed
Advance And Read signal was blocked so that no further Forward Step
signals were generated.
Consider next the operation of the circuitry when it is desired to
read the next Word. In this instance, after first depressing the
Read Next pushbutton in FIG. 4, the operator depresses the Word
pushbutton in FIG. 5. Depression of the Word pushbutton results in
the application of a triggering impulse to Word flip-flop 5-WORD.
Once again, it will be noted that this flip-flop is set-steered and
therefore it will switch to a set condition. In the present
instance, since it is desired than an entire word be read and
because more than one character may make up a word, it is necessary
to permit more than one character to be read. Thus the signal to
stop the Reader (i.e., block and Advance And Read signal by
resetting flip-flop 8-SS) must be derived not from the sprocket
signal as in the previous case, but from the decoding of one of the
nonprinting characters which normally signal the end of a word.
Typically, some of these characters are "Space," "Horizontal Tab,"
"Carriage Return," and "Line Feed." Other such characters of
signals will be obvious to the reader and decoding circuits for
detecting the presence of such characters may easily be developed
following the teachings of the circuitry shown in FIGS. 7A through
7C.
Gates 8-20 through 8-24 associated with the reset-steering input of
the Stop Strobe flip-flop 8-SS provide the necessary control for
resetting this flip-flop under the desired conditions. It will be
apparent that these gates are arranged in order to insure that the
flip-flop 8-SS has a logic 0 signal applied to its reset-steering
input when either the Word or Line flip-flop 5-WORD and 5-LINE are
energized, and there is a Carriage Return, a Space, a Horizontal
Tabulation, or an Off signal read from the tape. Under these
conditions, the subsequently appearing Forward Step signal from the
output of gate 8-47 will be applied as a trigger pulse to reset
Stop Strobe flip-flop 8-SS. In the event that the Line pushbutton
is pressed, there is a similar action in order to permit an entire
line to be read. In this instance, only the presence of a Carriage
Return signal can be operative to block further reading. This is
effected by means of the gates 8-20, 8-21, and 8-22 associated with
the reset-steering input of the Stop Strobe flip-flop 8-SS. Thus,
the gate 8-20 will apply a logic 0 to one input of gate 8-21 when
either the Line or Word pushbutton is pressed; in addition, the
decoding of a Carriage Return signal will result in a logic 0
applied to the other input. Accordingly, gate 8-21 produces a logic
1 at the output thereof which causes the logic 0 at the output of
attached gate 8-22 to reset steer flip-flop 8-SS.
OMIT NEXT OPERATION
Another aspect of tape-editing operations that can be extremely
important is the facility for omitting either the next character,
word, or line in a previously prepared tape. With the present
invention, this is accomplished by first pressing the Omit Next
pushbutton appearing at the lower central portion of FIG. 4. This
provides a logic 1 set signal which switches the Omit Next
flip-flop 4-ON to a set condition. It simultaneously insures, via
suitably oriented diode 4-31 and lead 4-30, that companion
flip-flops 4-RN and 4-BS are placed in a reset state. The logic 1
signal appearing at the set output of flip-flop 4-ON is immediately
applied to one of the inputs of gate 5-16 in order to prevent the
previously described reading action which would be initiated
through gate 2-13 in FIG. 2.
The amount of material to be omitted is then selected by operating
either the Character, Word, or Line pushbuttons in FIG. 5. The
operation of the circuitry in response to the subsequently applied
signals is substantially similar to that which occurred when
reading was involved. Thus, first flip-flop 5-OMIT is set. Upon
setting, the logic 1 signal appearing at the output of flip-flop
5-OMIT is applied to the set input of flip-flop 8-SS switching it
to a set condition. Gate 8-25 is connected to the reset output of
flip-flop 8-SS and it receives a full complement of logic 0 inputs
upon the next occurring CP1 clock pulse. It may be noted that
during Read Next operation, the appearance of the 4-RN signal on
one of the inputs to gate 8-25 blocked its operation. The logic 1
provided at the output of gate 8-25 is operative through gates
8-13, 8-14, 8-15, and 8-47 to produce Forward Step pulses for
application to the reader.
In contrast with the previously described usual operations, in this
mode of operation the forward step pulses are repetitively
generated at a high frequency, without reliance upon synchronizing
signals RNC from the Teleprinter. These pulses recur at the
repetition frequency of the Clock Pulse Generator 2-CPG I. The Tape
Reader stepping action will continue until flip-flop 8-SS is reset.
The resetting of the latter flip-flop is accomplished in the manner
aforedescribed and depends upon whether or not the Character, Word,
or Line pushbutton is actuated.
SKIP DELETES
There are times, as previously explained, when the "Delete"
character is used to obliterate other characters which were
originally inserted into the tape in error. In these cases, it is
advantageous not to read the Delete since time is wasted. Instead,
it is preferable to omit them in a manner similar to the omission
operation just described. In order to effect this type of omission,
a Skip/Deletes switch is provided. This switch is shown in the
upper right portion of FIG. 8. As arranged in this embodiment of
the invention, when it is desired to skip/delete characters, the
switch is opened. When system is in either the Run or Read Next
operating modes, a logic 0 will be presented through gate 8-26 to
one of the inputs of gate 8-27. Another logic 0 is provided to the
input of gate 8-27 as a result of the connection through resistor
8-29. When the Decoding circuitry detects the presence of a Delete
character as the reader, the third input of gate 8-27 receives a
logic 0 thereon and this results in a logic 1 being presented at
the output. Gates 8-28 and 8-30 are responsive to this logic 1 to
provide a logic 1 setting pulse to the Delete flip-flop 8-DEL.
The setting of flip-flop 8-DEL presents a logic 0 to one of the
inputs of gate 8-34. Another input of gate 8-34 is supplied via
gates 8-31, 8-32, and 8-33. When a Delete character is detected
these gates provide a logic 0 enabling signal to gate 8-34 and it
thereafter passes CP1 clock pulses as long as flip-flop 8-DEL
remains set. The resulting logic 1 pulses on lead 8-35 are applied
to one of the inputs of gate 8-13 and initiate generation of
Forward Step pulses at the repetition rate of Clock Pulse Generator
2-CPG I.
After the institution of this Skip/Deletes operation, when a
character other than Delete is presented at the Tape Reader,
flip-flop 8-DF is set steered due to the removal of the logic 1
that the Delete signal applied to the input of gate 8-31. At this
time, the output of gate 8-31 is a logic 1. The presentation of
this logic 1 to the input of gate 8-32 results in the generation of
a logic 0 at its output which is applied to the set-steering lead
of the Delete Finish flip-flop 8-DF. Since Delete flip-flop 8-DEL
is in a set condition, it presents a logic 0 to one input of gate
8-36. The subsequently occurring CP1 clock pulse therefore passes
through gate 8-36 and triggers the Delete Finish flip-flop 8-DF to
a set state. Upon setting, flip-flop 8-DF resets flip-flop 8-DEL
via lead 8-37. This prevents the passage of further clock pulses
via gate 8-34 and lead 8-35. When flip-flop 8-DF is set, the set
output is also applied to gate 8-10 to restore the control system
to normal reading operation.
PARITY EDIT OPERATION
When a tape is developed in response to received data, it
conventionally includes parity codes indicating whether or not the
preceding block of data satisfies a parity check. If the block of
data is correct, an "ACK" code will be inserted. If the data is
incorrect, a "NAK" code will be inserted. When the tape is being
edited, it may be submitted to the TApe Reader in reverse order so
that the status character (ACK or NAK) will be read before the
associated block of data. The present invention provides means for
selectively omitting blocks of characters which are preceded by a
NAK code.
In FIG. 8, the Parity Edit switch appears in the lower left
quadrant. When this switch is open, the control system will omit
data preceded by NAK characters. The decoding of a "NAK" character
results in gate 3-38 having logic 0 at both inputs; consequently, a
logic 1 appears at the output thereof and this is inverted by gate
3-39 and applied as the set steering input of Omit Next Block
flip-flop 8-ONB. Flip-flop 8-ONB is set upon the application of the
Strobe In signal from the Teleprinter. It will be recalled that the
appearance of this signal indicates that the auxiliary device has
received and digested the previous character. This triggering pulse
provides a convenient timing pulse to assure that the "NAK" signal
has reached equilibrium prior to switching flip-flop 8-ONB. When
flip-flop 8-ONB is set, the logic 1 at its set output is applied to
gate 8-31. As in the case of the detection of a Delete signal from
the Decoding circuitry, this results in the delivery of pulses at
the repetition rate of Clock Pulse Generator CP1 over lead 8-35 to
gate 8-13. Accordingly, Forward Step pulses are supplied at this
rapid rate to the Tape Reader. The high-speed skipping action will
continue until the Omit Next Block flip-flop 8-ONB is reset.
The resetting action is initiated by detecting the presence of an
"ACK" code in the tape. This code sets flip-flop 8-ACKS by placing
a logic 0 on the set steering input thereto. The logic 0 is applied
via gates 8-43 and 8-44. It will be seen that gate 8-43 has both
inputs at logic 0 when flip-flop 8-ONB is in a set state and the
"ACK" signal is detected by the Decoding circuitry. When flip-flop
8-ACKS is set upon occurrence of the next Forward Step pulse, it
presents a logic 0 to the input of gate 8-45. The other input to
gate 8-45 is a logic 0 when the presence of an "ETB" or "ETX" code
is detected. By international standards, the latter codes are
positioned next to the "ACK" code and will accordingly in this
instance follow the "ACK." Thus, a logic 1 signal is generated at
the output of gate 8-45 which sets search for "NAK" flip-flop 8-SFN
and resets Omit Next Block flip-flop 8-ONB. The setting of
flip-flop 8-SFN restores the Reader to normal operating conditions
by applying a logic 1 to the set input of the Start Reader
flip-flop 2-SR, thereby initiating generation of the Start Reader
signal.
REMOTE CONTROL OPERATION
It will be appreciated that there are times when the Teleprinter is
being used to transmit data to a remote unit. At these times the
data may be checked for errors at the remote site and the coded
"ACK" or "NAK" signals returned to the Teleprinter to indicate
satisfactory or unsatisfactory transmission respectively. When
transmitting from the Tape Reader, it must be stopped until the
check for errors has occurred and then resume upon receipt of
"ACK." If the check shows an error and "NAK" is returned to the
sender, the Reader must be reversed and the previous block of data
reread and retransmitted.
If the Teleprinter is employing error detection, it will provide a
logic 1 signal labeled 9-BCCF to gate 4-22 in FIG. 4B at the time
the Reader is to be stopped. This stops the Reader in the same
manner as the Tape Out condition previously described.
It will be appreciated that when the Teleprinter is being operated
in this fashion, the control system will be either in a Run or a
Read Next mode. FIG. 9 contains the principal logic elements for
effecting the desired controls in the particular situation
envisaged. As shown in this figure, flip-flop 9-BCCR is set when
the control system is in a Run mode and flip-flop 9-BCCRN is set
when the system is in a Read Next mode. This is established by set
steering the flip-flops with signals from the set outputs of the
Run flip-flop 2-Run and the Read Next flip-flop 4-RN, respectively.
The BCCF signal from the Teleprinter is used as a trigger signal
for these flip-flops.
If the Teleprinter determines that it is advisable to repeat a
block of data, it provides a reverse signal (REV) which is applied
to the input of gate 9-15. Gates 9-13 and 9-14 are appropriately
interconnected to the outputs of flip-flop 9-BCCR and 9-BCCRN so
that at least one of these flip-flops must be set in order to
provide a logic 0 output on gate 9-14. Gates 9-14 and 9-15 both
supply the input to gage 9-16. When both inputs are at logic 0,
gate 9-16 provides a logic 1 output which is inverted in gate 9-17
to provide a Trigger Start Reverse signal on lead 9-18 which will
initiate reverse stepping of the Reader. This signal is applied to
gates 2-16, 2-19 and 2-21 appearing along the left-hand edge of
FIG. 2.
In order to prevent an endless cycle of read-error-reverse, a
binary counter is provided in the form of flip-flops 2-A and 2-B
illustrated in the lower center portion of FIG. 2. Flip-flop 2-A is
set on the first repeat of data; flip-flop 2-B is set on the second
repeat of data. The outputs of these flip-flops are applied to
gates 2-16 and 2-20 in order to control the effect of the Trigger
Start Reverse signal on the Tape Reader.
Assuming that the first repeat of data is requested and therefore
the counter has not achieved its maximum count, gate 2-20 will set
steer the Start Reverse flip-flop 2-SREV. When the Start Reverse
flip-flop 2-SREV is thus set steered, the Trigger Start Reverse
signal will be applied through inverter gate 2-19 to trigger the
flip-flop into a set condition. The resulting logic 1 signal on the
set output of the Start Reverse flip-flop 2-SREV is transmitted via
lead 2-30 to the set input of Reverse flip-flop 2-R. The logic 1
appearing at the set output of reverse flip-flop 2-R is then
applied to gate 2-31 which also receives an input from the set
output of Back Step flip-flop 2-BSF. The resulting logic 0 at the
output of gate 2-31 is applied to the input of gate 2-32 and is
effective to enable this gate to pass CP1 clock pulses as Reverse
Step pulses to the Tape Reader. When the tape Reader is run in
reverse, it will continue to do so until the Reverse Step pulses
stop. This occurs when an "SOH" or "STX" character code is detected
in the tape. Those familiar with the ASCII code will recognize that
these character codes indicate the start of a block of data.
When one of these codes, or the reader tape out condition occurs,
the output of gate 2-33 becomes a logic 0 and reset steers Reverse
flip-flop 2-R. Flip-flop 2-R is triggered by CP2 clock pulses and
thus resumes the reset condition upon the next occurring CP2 pulse.
Upon resetting, the reset output of flip-flop 2-R is applied as a
trigger to set Start Run flip-flop 2-SRU. The set steering of the
latter flip-flop will be explained hereinafter. When flip-flop
2-SRU is set, it reinitiates the Run mode by setting Run flip-flop
2-RUN via gates 2-17 and 2-18.
If a second "NAK" signal is received after repeating the data, this
will result in increasing the count stored in flip-flops 2-B and
2-A. When the third "NAK" is received, the respective states of
these counter flip-flops prevent the setting of the Start Reverse
flip-flop 2-SREV and instead enable the set input of Run flip-flop
2-RUN. Thus, the system is returned to the Run mode without causing
further reversals.
If, after a block has been transmitted, the Reader being at rest,
an "ACK" signal is received from the remote unit, the Teleprinter
will provide a signal of logic 1 value at the input of gate 2-23.
This is effective to reset both counter stages 2-A and 2-B. The
counter is also reset through gate 2-21 after it has reached the
maximum allowable count. In the latter case, this resetting is
accomplished upon coincidence of the Trigger Start Reverse and the
set condition of Start Reader flip-flop 2-SR. The receipt of an
"ACK" signal also results in the Teleprinter generating a forward
(FWD) signal which is applied to gate 9-12 in FIG. 9. The FWD
signal in combination with an indication that the Read Next
flip-flop 9-BCRN is in a reset condition and that the Run flip-flop
9-BCCR is in a set condition will result in the generation of a
logic 1 signal at the output of gate 9-13 which is used to set
Start Run flip-flop 2-SRU in FIG. 2.
The above-described sequence of operation assumed the equipment was
initially in a Run mode. In the event that the equipment is in the
Read Next mode, a similar sequence of operation will occur. The
difference resides in the fact that rather than having flip-flop
9-BCCR set, the Read Next flip-flop 9-BCCRN will be set. Under
these conditions, the system will be restored to the Read Next mode
by flip-flop 9-BCCRN and interconnected flip-flop 2-SRN in FIG. 2.
It is believed unnecessary to specifically trace the details of the
latter circuitry in view of the fact that all of the interconnected
gates have been considered in connection with resuming operation
under the Run mode.
BACKSPACING
This control system also provides for normally controlled
backspacing of the Reader. The manner in which the Reverse Step
signal is generated in response to the Teleprinter command has been
explained. In order to that generation of this signal within the
control circuit itself, the Backspace Pushbutton appearing in the
lower right quadrant of FIG. 2 is provided. When this pushbutton is
depressed, it applies triggering pulses from clock pulse generator
CPG I to Backspace Pushbutton flip-flop 2-BSPB. The setting of the
latter flip-flop provides a trigger signal to Backspace flip-flop
2-BSF and this in turn is set. Upon being set, flip-flop 2-BSF
applies a logic 1 signal to the input of gate 2-31 and as
previously described, this results in the application of a Reverse
Step pulse to the printer at the output of gate 2-32. The next
occurring CP1 clock pulse resets flip-flop 2-BSF and when the
pushbutton resumes its initial position, flip-flop 2-BSPB is reset.
Thus, a single step in the reverse direction is made.
In order to insure that the other modes are not disturbed during
this type of backspace operation, the output of flip-flop 2-BSF is
applied to the set input of backspace flip-flop 4-BS, the latter
flip-flop being reset whenever any of the other modes are
initiated.
A specific tape control system has been described and illustrated.
This tape control system was illustrated in an embodiment utilizing
specific logic circuitry in order to effect the necessary
functions. It will be appreciated that those skilled in the art are
capable and expected to modify this logic circuitry in accordance
with the particular needs of the equipment with which they are
working. The scope of the invention is intended to include all
modifications that come within the spirit and teachings of this
disclosure.
* * * * *