U.S. patent number 3,633,166 [Application Number 05/034,781] was granted by the patent office on 1972-01-04 for data transmission method and serial loop data transmission system.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Jean L. Picard.
United States Patent |
3,633,166 |
Picard |
January 4, 1972 |
DATA TRANSMISSION METHOD AND SERIAL LOOP DATA TRANSMISSION
SYSTEM
Abstract
A method and system for transmitting data between a central
control unit and a plurality of terminals arranged in a loop
configuration in which each terminal includes a shift register and
a two-position switch, the former short circuiting the terminal and
the latter interposing the shift register in the loop. When the
central unit wants to know which terminals have data to transmit to
it, it sends a B character on the loop, which is intercepted by the
registers of all the terminals. The terminals which have data to
transmit place their switch in its second position and load their
register with their identification number. The central unit then
sends a sequence of A characters which are intercepted by the
terminals which have their switch in the second position and which
shift the identification numbers from register to register and so
forth to the central unit, thus enabling the central unit to
determine which terminals have data to transmit.
Inventors: |
Picard; Jean L.
(St-Laurent-du-Var, FR) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
9033911 |
Appl.
No.: |
05/034,781 |
Filed: |
May 5, 1970 |
Foreign Application Priority Data
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|
|
|
|
May 16, 1969 [FR] |
|
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6915337 |
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Current U.S.
Class: |
370/395.1;
340/12.21; 370/452 |
Current CPC
Class: |
H04L
12/423 (20130101) |
Current International
Class: |
H04L
12/423 (20060101); H04q 005/00 (); H04q 009/00 ();
H04q 011/00 () |
Field of
Search: |
;340/163 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pitts; Harold I.
Claims
1. A method for establishing communications between a central
station and a plurality of remote stations connected in a serial
loop with said central station comprising the steps of:
transmitting from said central station, characters having a first
predetermined bit configuration followed by at least one character
of a second predetermined bit configuration and immediately
followed by characters having said first predetermined bit
configuration;
at each said remote station monitoring the bit configurations on
the loop for detecting the presence of said second predetermined
bit configuration;
inserting a unique bit configuration identifying the remote station
following the detection of said second predetermined bit
configuration when the station has data to send to the central;
buffering a predetermined number of incoming bits from the loop
before passing the buffered bits onto the next remote station on
the loop;
monitoring the buffered bits to detect the said first predetermined
bit configuration; and
passing the received bit stream directly onto the next remote
station in the loop when the said first predetermined bit
configuration is detected amongst the buffered bits whereby said
central station receives from the last station in the loop a
plurality of unique bit configurations, each identifying one remote
station which has data to send to the central and requires service
which may be initiated by the central in any order which is
appropriate since the central is advised of all remote stations
2. A method for establishing communications between a central
station and a plurality of remote stations connected in a serial
loop with said central station comprising the steps of:
transmitting from said central station characters having a first
predetermined bit configuration followed by at least one character
of a second predetermined bit configuration and immediately
followed by characters having said first predetermined bit
configuration;
at each said remote station;
monitoring the bit configurations on the loop for detecting the
second predetermined bit configuration,
inserting a unique bit configuration identifying the remote station
following detection of the said second predetermined bit
configuration when the remote station has data to send to the
central station,
following detection of the said second predetermined bit
configuration buffering a predetermined number of incoming bits
from the loop before passing the buffered bits onto the next remote
station on the loop,
monitoring the buffered bits to detect the said first predetermined
bit configuration, and
passing the received bit stream directly onto the next remote
station in the loop when the said first predetermined bit
configuration is detected whereby the said central station receives
from the last remote station in the loop a plurality of unique bit
configurations each identifying one remote station which has data
to send to the central in the inverse order of their physical
arrangement on the loop preceded by the said second predetermined
bit configuration and followed by said first predetermined bit
configuration, and
at said central station after receipt of said unique address
followed by said first predetermined bit configuration transmitting
a third predetermined bit configuration followed by a unique remote
station address from amongst the unique station addresses received
for enabling the addressed remote station to send data via the loop
to the central station and repeating the sequence until all
stations needing service have
3. A communications system for providing data transmission between
a central station and a plurality of remote stations connected in a
serial loop with said central station comprising:
means at said central station for transmitting characters having a
first bit configuration followed by at least one character having a
second bit configuration and immediately followed by characters
having said first bit configuration;
input means at each remote station for receiving data bits from the
preceding station;
output means at each remote station for transmitting data bits to
the next succeeding station;
shift register means at each remote station connected to the input
means for registering a predetermined number of consecutive
bits;
switch means for alternatively connecting the shift register to the
output means in one state and the input means directly to the
output means in its other state;
decoder means responsive to the contents of said shift register for
detecting the said first and second bit configuration and providing
outputs indicative thereof; and
control means responsive to the output indicative of the detection
of the second bit configuration for causing said switch means to
assume its said other state and for inserting a unique station
identification code in the said shift register over the previously
received said second bit configuration and for causing said switch
means to assume its said first state when the output from the
decoder means indicates the reception of the said first bit
configuration whereby said central station receives from the output
means of the last remote station on the loop a plurality of unique
bit configurations each identifying one remote station which has
data to send to the central and requires service which may be
initiated by the central in any appropriate order since the central
is advised of all
4. A communications system as set forth in claim 3 in which the
first and second bit configurations and said unique station
identification codes all
5. A method for establishing communications between a central
station and a plurality of remote stations connected in a serial
loop with said central station comprising the steps of:
transmitting from said central station characters having a first
predetermined bit configuration followed by at least one character
having a second predetermined bit configuration immediately
followed by characters having said first predetermined bit
configuration;
at each said remote station buffering a predetermined number of
incoming bits from the loop before passing the buffered bits onto
the next station on the loop;
monitoring the buffered bits for detecting the presence of said
first bit configuration following the second bit configuration;
and
inserting a unique bit configuration identifying the remote station
when the station has data to send to the central station in place
of the said first bit configuration which follows the said second
bit configuration whereby the central station receives from the
last remote station in the loop a plurality of unique bit
configurations each identifying one remote station which has data
to send to the central station and requires service which may be
initiated by the central in any order which is appropriate since
the central is advised of all remote stations requiring service.
Description
BACKGROUND OF THE INVENTION
This invention relates to a method for transmitting data between a
transmission control unit and a plurality of serially connected
terminals arranged in closed loop.
As the business expands, many loan companies or banks have been
forced to open geographically separated branches so that their
customers may, without inconvenience, complete transactions. But
with such widely separated network of it becomes more difficult to
complete transactions in any one branch. Thus, if a customer has an
account in one branch and if he wants to make a transaction at
another one, the clerk of the bank will have to call the former in
order to obtain information relative to the customer account in
order to complete the transaction.
Therefore, it is necessary to unite such a network of branches by
creating a central office wherein all the transactions completed by
the different branches may be centralized. In the case of a network
of banks, for instance, all the customers will have their bank
accounts at the central office, and any credit or debit operation
made in a branch will automatically be sent to the central office
in order to update the account of the customer as a transaction is
completed.
The central office is generally provided with one or more
computers, which will be called hereinafter "transmission control
unit," having a very large capacity disk or tape units for
memorizing all the incoming information. The transmission control
unit communicates with the branches through telephone cables, by
means of modulator-demodulator systems, or modems, which are
well-known in the art. In a like manner, in each branch, a terminal
which operates the various incoming transaction machines, transmits
the information over the same telephone lines via the modems.
DESCRIPTION OF THE PRIOR ART
In the prior art, a plurality of systems have been used to connect
the transmission control unit to the different terminals.
In a first system, the terminals are radially connected to the
transmission control unit. This is the so-called "point-to-point"
configuration. Such a system requires one modem per line at the
transmission control unit and one modem per terminal. The cost of
all these modems is a high percentage of the total cost of the
installation.
Another well-known system, the so-called "multiple terminals"
configuration, consists in connecting in parallel all the terminals
on a single line. This reduces the total number of the modems used
since only one modem is required at the transmission control unit.
Such a system is wasteful of transmission capacity since it must
start its modulator before it can start transmission.
A third well-known system, the so-called "loop" configuration can
be used. In such a system, the terminals are connected in series by
a single line coming from and leading back to the transmission
control unit. The line reaches each terminal through the
demodulator of a modem and leaves it through the modulator of the
same modem. Thus, the information sent over the loop goes through
each of the modems. Said modems, therefore, are always in
operation. This avoids the loss of time mentioned previously with
regard to the "multiple terminals" configuration.
In the "loop" configuration, it is obvious that several terminals
cannot communicate simultaneously with the transmission control
unit. When a terminal wants to transmit a message, the other
terminals must therefore be informed that the loop will be
occupied. A prior art method sends a plurality of predetermined
instruction characters over the loop from the transmission control
unit, which enables the first rank terminal on the line which wants
to transmit a message to the transmission control unit, to get
ready for a transmission operation and which controls the switching
off of the other terminals. Once this terminal has transmitted its
message, it sends the same predetermined instruction characters as
previously and the next following terminal which wants to send a
message in its turn, can be operated. With such a method, once the
transmission control unit has informed the first terminal that it
may proceed to complete a transmission, and this due to the
predetermined instruction characters, data transmission is under
the control of the various terminals, in sequence of physical
arrangement and control is not restored to the transmission control
unit. Furthermore, the transmission order of the terminals is
determined solely by the rank or physical position they occupy on
the loop which makes the use of some terminals in priority over
others impossible.
SUMMARY OF INVENTION
Therefore, one object of the invention is to provide a data
transmission method between a transmission control unit and a
plurality of terminals, wherein the transmission control unit
reassumes control of transmission after each terminal has completed
a single transmission.
Another object of the invention is to provide a data transmission
method between a transmission control unit and a plurality of
terminals, wherein the control unit can request a priority
transmission of any terminal over the others.
The objects of the invention are fulfilled in a preferred
embodiment wherein each terminal includes a register and a
two-position switch, the first position short circuiting the
terminal, the second one inserting the register into the loop. When
there is no information from or to the transmission control unit,
the switch is in its first position and the transmission control
unit is continuously sending characters of a first configuration
over the loop. When the transmission control unit wants to know
which terminals are in a condition to transmit information to it,
said unit sends a character of a second configuration which is
received by each terminal. The terminals which have information to
be transmitted to the transmission control unit then, switch their
switches into their second positions and transfer their
identification code or character to their registers, respectively.
Then, the transmission control unit continuously sends first
configuration characters over the loop. The terminal identification
characters are thus transferred from one register to the next one
onto the transmission control unit, the terminal switches being
respectively switched into their first positions when the first
character of the first configuration is received in the
corresponding register. It should be noted that after the second
configuration character, the transmission control unit can
continuously send characters of a third configuration, said
characters being used only for the transfer of the identification
numbers from one register to the next one. Therefore, the
transmission control unit receives the series of the identification
character of all the terminals which want to transmit information
to the control unit, which enables said unit to start data
transmission of the different terminals according to a transmission
order chosen by it while reassuming control of the transmission of
data after each terminal completes transmission.
The foregoing and other objects, features and advantages of the
invention will be apparent from the following more particular
description of preferred embodiments of the invention, as
illustrated in the accompanying drawings.
In the drawings:
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a data transmission system which makes use of the "loop"
configuration.
FIG. 2 is a simplified diagram of a terminal for communication on
the loop according to the preferred embodiment of the
invention.
FIG. 3 is a table showing the different characters received and
transmitted by a terminal according to a preferred embodiment of
the invention.
FIG. 4 is a simplified diagram of a terminal for communication on
the loop according to another embodiment of the invention.
FIG. 5 is a table showing the characters received and transmitted
by the terminals on the loop according to the preferred embodiment
shown in FIG. 4.
FIG. 6 is a simplified diagram of a terminal for communication on
the loop according to another embodiment of the invention.
FIG. 7 is a table showing the characters received and transmitted
by the terminals on the loop according to the preferred embodiment
shown in FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is the general arrangement of a data transmission system in
a closed circuit, the so-called "loop" configuration.
The transmission control unit 2, or TCU, sends data over the closed
circuit 4 via a modulator. Said modulator is part of the
modulator-demodulator system, or modem. Likewise, the TCU receives
the data from the circuit via the demodulator of modem 3. As shown
in the figure, a plurality of terminals A, B, C, ... can be
arranged in the closed circuit. For instance, if reference is made
to terminal A, it can be observed that the data sent from the TCU 2
passes through the demodulator of modem 11 and are then received in
the control unit 12. Said control unit can operate on its own a
plurality of input-output stations 13, 14, 15, ... generally placed
at the same geographical location. Said stations which include the
devices for the introduction of the operated transactions are not
part of the invention, and therefore, they will not be described
here.
The above used term "transmission control unit" may designate any
device provided with a memory and a control unit capable of
handling data transmission and data reception, such as a computer
provided with adequate peripheral units, a communication
controlling device or a line concentrator.
The preferred embodiment of the invention will now be described
with reference to FIG. 2. This figure shows a terminal in a
schematic form. The main units for the embodiment of the invention
are a shift register 20 the capacity of which corresponds to the
format of the characters used during the transmission wherein the
data are received or transmitted bit after bit over the loop and a
switch 24 with two positions 25 and 26. Position 25 is used to
short circuit the terminal and position 26 causes the data to pass
through register 20. While switch 24 has been shown in a simplified
manner, it is obvious because of the rate of the data flow that it
will include electronic circuits which are well known in the
art.
Except for the data transmission to or from the terminals, the
transmission control unit sends continuously characters of
configuration A over the loop. If, for instance, the data
transmission is made according to the synchronous mode, these
characters are synchronization characters which cause the terminals
to get synchronized with the TCU. As long as the A configuration
characters are being received by the terminal, switch 24 is in
position 25.
When the TCU wants to know which terminals desire to transmit
information to it, it then sends a character of a second
configuration B. This B configuration character is sent all along
the loop since the terminal switches are in positions 25,
respectively. But this character is also loaded bit after bit in
the shift register of each terminal. When the entire character is
loaded in register 20, it is parallel decoded by a decoding device
21 and the result is transmitted to the control device 23. Should
the terminal have information to be communicated to the TCU, then
the device 23 controls two operations, namely the parallel transfer
of the identification number of the terminal from a memory 22 to
register 20 on the one hand and the switching of switch 20 which
switches from position 25 to position 26 on the other hand. If
transmission is not required, switch 24 is maintained in position
25. These decoding and control operations are achieved within a
very short time period with respect to the time duration of a bit.
Since the sampling of the bits is made at about the midtime of the
time period of a bit, there is enough time left after the sampling
of the last bit in the character to complete all these decoding and
control operations.
After the transmission control unit has sent the B configuration
character, it resumes sending the A configuration characters. The
transmission control unit could send characters having another
configuration over the loop without modifying in any way the rest
of the procedure. Since the terminals which had no information to
be transmitted to the TCU have maintained their switches in
positions 25, respectively, they are of no interest in the
following description since they are short circuited. On the
contrary, the first terminal which has its switch 24 in position 26
receives the first A configuration character transmitted by the
TCU. As this character is being loaded into shift register 20, the
identification character is transmitted bit after bit over the loop
through line 27 due to switch 24 being in position 26. In the
meantime, the bits of the identification character of this first
terminal are loaded in the shift register of the second terminal
having its switch in position 26 (or in other words, having
information to be transmitted). Likewise, as the bits are arriving,
the identification character of this second terminal is transmitted
over the loop and so on. Therefore, there is a step-by-step shift
and the transmission control unit receives the identification
character of the last terminal of the loop that desires to transmit
information.
Once the A configuration character has been loaded in the shift
register of the first terminal, it is decoded by decoder 21 and
control device 23 causes switch 24 to transfer from position 26 to
position 25. On the other hand, no change in the switch positions
occurs in the following terminals which receive the identification
number of the preceding terminal which desires to transmit
information since it is not an A configuration character which has
been decoded.
When the transmission control unit sends the second character of
configuration A, it is received by the second terminal which
desires to transmit information. The shift of the identification
characters occurs in like manner as seen previously, and the
transmission control unit therefore receives the identification
character of the next to last terminal on the loop that desires to
transmit information. Likewise, upon reception of the A
configuration character, the terminal which received it switches
its switch back to position 25, thus causing the next A
configuration character to reach directly the next terminal which
has its switch in position 26.
In this embodiment, it has been supposed that the terminal
identification codes were represented by a single character, but
they could be assumed as being represented by a plurality of
characters. In this case, each terminal will be provided with a
buffer memory containing the different characters of the
identification code before transmitting them via register 20.
Therefore, the transmission control unit receives consecutively,
all the identification characters of the terminals having
information to be transmitted according to an order which is
opposite to their respective geographical positions on the loop.
Said unit sends A configuration characters until it receives an A
configuration character which is immediately following the last
identification character corresponding to the geographically first
terminal having information to be transmitted. The reception of
this character indicates to the transmission control unit that it
has received all the identification characters of the terminals
desiring to transmit information. At this time, the TCU may ask any
one of said terminals to transmit its information. Contrary to the
prior art devices, the first terminal on the loop will not
necessarily be the first to transmit its information. The
information control unit has only to send a C configuration
character followed by the identification number of the selected
terminal. The addressed terminal will cause switch 24 to move to
position 26. Then, the terminal will load the shift register 20
with the information characters coming from memory 22. The
continuous sending of A configuration characters will cause
register 20 to send said characters over the loop bit after
bit.
For a better understanding of the preferred embodiment of the
invention, reference is made to FIG. 3. In this figure, it is
supposed that there are five terminals on the loop. From amongst
these five terminals, only three have information to be transmitted
to the transmission control unit, namely terminals 1, 3, 5 having
identification numbers No. 1, No. 2, No. 3, respectively. It is
obvious that these numbers are given only for a descriptive purpose
and that, in fact, a number is represented by a single character of
a specific configuration (or by a group of several characters as
mentioned previously). In FIG. 3, the first column indicates the
succession of the characters transmitted from the TCU and the last
column, the succession of the characters received by the TCU. For
each terminal, the contents of the register 20 at the end of the
reception of a character are indicated on the one hand, and the
position of switch 24 at the end of the reception of this very
character is on the other hand. It can be observed, as seen
previously, that the TCU receives first the B configuration
character, then the succession of the identification numbers of the
terminals having information to be transmitted according to an
order opposite to their respective geographical positions on the
loop, the A configuration characters which indicate that the TCU
has duly received all the identification numbers of the terminals
having information to be transmitted.
It is possible to envisage a variation of the invention by making
use not only of a single shift register as seen in the previous
embodiment, but of two shift registers. In that case, with
reference to FIG. 4, it can be seen that register 30 receives the
characters coming from the transmission control unit, however, it
is register 38 which is loaded from memory 32 with the characters
that the terminal is transmitting to the TCU. As seen in the
previous embodiment, the transmission control unit sends one B
configuration character in order to ascertain which terminals have
information to be transmitted. The B configuration character is
received in register 30, is decoded by decoding device 31 and
should the terminal have information to be transmitted, the control
device 33 which receives the decoding information from device 31,
controls the parallel transfer of the identification number of the
terminal from memory 32 to register 38 at the end of the reception
of the B configuration character in register 30. In the same time,
the device 33 controls the change in position of the switch 34
which passes from position 35 to position 37. Thus, all the
terminals having information to be transmitted to the TCU have
their switches in positions 37 and have loaded register 38 with
their identification character, respectively. After sending the B
configuration character, the transmission control unit resumes
sending A configuration characters. If the first terminal on the
loop ready to transmit information is considered, it will receive
an A configuration character. As the register 30 is being loaded
with this character bit after bit, the terminal proceeds to the
sending of its identification number bit after bit from register 38
via position 37 of switch 34. Once the transmission of the
identification number is over, the terminal switches its switch to
position 35. On the other hand, the second terminal having
information to be transmitted receives the identification number of
the previous terminal in its register 30 as it is transmitting its
identification number from register 38. But because this terminal
does not receive any A configuration character from its register
30, its switches its switch 34 to position 36. The same holds true
for each of the following terminals having information to be
transmitted which switch their switches 34 to positions 36,
respectively. For the rest of the procedure, the preferred
embodiment of the invention is considered anew with a two-position
switch.
The example shown in the table of FIG. 5 is used for a better
understanding of the above explained embodiment. In this example,
it has been supposed that the terminals 1 and 3 have information to
be transmitted from amongst the three terminals on the loop. In
this embodiment as in the previous one, the transmission control
unit receives the identification numbers of the terminals according
to an order opposite to their geographical positions on the
loop.
In this embodiment, it should be noted that if the transmission is
carried out in the "start-stop" mode, it is the detection of the
first bit in the character, i.e., the bit "start" received in
register 30 by device 31, that will enable device 33 to control the
beginning of the transmission, bit after bit, of the identification
number contained in register 38. Whereas in the "synchronous" mode
wherein the characters are occupying consecutive time intervals,
the transmission of the identification number contained in register
38 is made without taking the bits received in register 30 into
account.
Once the TCU has all the identification numbers of the terminals
having information to be transmitted, it sends a C configuration
character followed by the identification number of the terminal
which is asked to transmit its information. But in this embodiment,
the designated terminal switches its switch to position 37 in order
to send the information characters from register 38.
Another embodiment of the invention will now be described with
reference to FIG. 6. As shown in this figure, the shift register is
directly on the loop and the characters coming from the
transmission control unit are transferred from one register to the
next one without being able to short circuit the terminals as seen
in the previous example. When the TCU sends a B configuration
character, this character is received by the register of the first
terminal on the loop. Should this terminal have no information to
be transmitted to the TCU, the decoding operation of the character
by decoder 41 entails no operation. On the contrary, should this
terminal have information to be transmitted, the decoding of the B
configuration character will cause the control device 43 to prepare
for the transfer of the identification number of the terminal from
memory 42 to register 40. But the identification character is
merely pending and it is only when the following A configuration
character sent by the TCU is loaded in register 40 that the
identification character is actually transferred in parallel into
the register 40. In the meantime, the B configuration character is
transferred into the register of the next following terminal. When
a terminal has information to be transmitted, it prepares its
identification character in order to transfer it into its register
40 when the first received A configuration character is decoded by
decoder 41. But, in fact, said second terminal will receive first
the identification character of the first terminal and it will
proceed to no operation. The first terminal identification
character will be transferred and only after decoding the following
A configuration character which immediately follows the
identification character of the first terminal will the second
terminal identification character be inserted. Thus, the sequence
of the identification numbers received by the transmission control
unit will correspond to the order of the terminals on the loop.
For a better understanding of the embodiment of the invention, an
example is shown in the table of FIG. 7. It is supposed that there
are four terminals on the loop and that only No. 1 and No. 3 have
information to be transmitted. The first column indicates the
character sent by the TCU and the columns corresponding to the
terminals indicate the character which is in the terminal register
after the character has been sent by the TCU. The last column
indicates the character received by the TCU after the same has
transmitted a character.
Though, in the preceding embodiments, the transmission control unit
wanted to know which are the terminals that have information to be
transmitted to it. It is obvious for the man skilled in the art
that the invention applies also to the case when the transmission
control unit has to transmit information to the terminals and must
know which are the ones of said terminals that are susceptible to
receive information.
While the invention has been particularly shown and described with
reference to preferred embodiments thereof, it will be understood
by those skilled in the art that the foregoing and other changes in
form and details may be made therein without departing from the
spirit and scope of the invention.
* * * * *