U.S. patent number 3,796,994 [Application Number 05/156,221] was granted by the patent office on 1974-03-12 for code communication system.
This patent grant is currently assigned to Edwards Company, Inc.. Invention is credited to Robert F. Nuss, Jr..
United States Patent |
3,796,994 |
Nuss, Jr. |
March 12, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
CODE COMMUNICATION SYSTEM
Abstract
A code communication system for interrogating remote stations
from a central station during successive communication cycles
wherein a start at a remote station is effective when received at
the central station to cause the central station to transmit in a
superiority search mode. Cycle reset means is provided governed by
a remote station having initiated a cycle by a start pulse for
causing the communication system to reset for starting a new
communication cycle whenever a bit of the code superiority address
transmitted from the central station disagrees in character with
the address code of the station having transmitted the start pulse.
Such a restart causes the transmission of another cycle which has
an address code bit changed in character for the last address bit
transmitted in the prior cycle. In this way an address code is
completed only for the most superior station having registered a
start.
Inventors: |
Nuss, Jr.; Robert F. (Shelton,
CT) |
Assignee: |
Edwards Company, Inc. (Norwalk,
CT)
|
Family
ID: |
22558635 |
Appl.
No.: |
05/156,221 |
Filed: |
June 24, 1971 |
Current U.S.
Class: |
714/750 |
Current CPC
Class: |
H04L
12/403 (20130101); H04Q 9/14 (20130101) |
Current International
Class: |
H04L
12/403 (20060101); H04Q 9/14 (20060101); H04q
009/00 () |
Field of
Search: |
;340/147LP,163 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pitts; Harold I.
Attorney, Agent or Firm: Kleinman; Milton E. Wynn; Harold
S.
Claims
1. A code communication system including at least one communication
channel for interrogating remote stations from a central station
during a communication cycle in response to a start pulse
communicated to the central station from one of the remote stations
and with each of the remote stations having an individual station
code assigned thereto and wherein the improvement comprises;
a. transmitting means at the central station response to a start
pulse communicated over the communication channel from the central
office to the remote stations a most superior station search
code,
b. receiving means at each of the remote stations for receiving the
search code transmitted by the transmitting means,
c. cycle reset means governed by a remote station having initiated
a cycle by transmitting a start pulse for causing the communication
system to be reset to start a new communication cycle in response
to the reception at that remote station of a search code bit that
has a sense that disagrees with a corresponding station code bit
assigned to that station, and
d. means at the central station responsive to the reset means for
activating the transmitting means to transmit another cycle
including the same address code as transmitted during the previous
cycle except that the sense is changed for the last search code bit
transmitted during the
2. A code communication system according to claim 1, and including
mode selecting means for selectively enabling the transmitting
means in a first mode to transmit successive roll call addresses
and in a second mode to
3. A code communication system according to claim 2 wherein the
mode selecting means enables the transmission of a most superior
station search code in the second mode in response to the start
pulse communicated from
4. A code communication system according to claim 3 wherein the
mode selecting means enables the transmission of addresses in the
first mode when no start pulse is received at the central station
from one of the
5. A code communication system according to claim 2 wherein:
a. means is provided for comparing each address code transmitted
from the central station during each roll call cycle with the
address code received at the central station over a common
communication channel from the remote station being interrogated
during that cycle and for delivering a recycle output signal when
the addresses compared are out of correspondence, and
b. means is provided for transmitting a distinctive address code
during successive roll call cycles from the central station to the
remote stations except that the same address code that was
transmitted during the
6. A code communication system according to claim 4 and including
limiting means for permitting the transmission of only a limited
number of repeat
7. A code communication system according to claim 6 wherein the
limiting means includes a trouble latch that delivers an output
after transmission
8. A code communication system according to claim 7 wherein the
output of the trouble latch advances the roll call of the
transmitting means to
9. A code communication system according to claim 8 and including
counting means for determining the order of transmission of roll
call addresses.
10. A code communication system according to claim 4 and including
alarm means responsive to the trouble signal for indicating the
detection of a
11. A code communication system according to claim 7 and including
alarm means that is activated by a trouble signal provided there is
an output of
12. A code communication system according to claim 1 having means
for selectively operating in roll call mode and in a code
superiority address search mode and having means for sequentially
selecting different station address codes for transmission over a
communication channel from a central station and having:
a. storage means for storing an address code for transmission to
the remote stations,
b. station counting means for counting roll call cycles of
operation and operable when enabled to deliver digital outputs to
the storage means in accordance with the station count
accumulated,
c. code setting means operable when enabled to set the storage
means to a most superior search address code, and
d. mode selecting means operable to select first and second modes
in response to signals from a remote station for enabling the
station counting and the code setting means, respectively, to
govern the address
13. A code communication system according to claim 12 wherein the
code setting means is enabled only for a first cycle of operation
of the system
14. A code communication system according to claim 13 wherein
toggle gating means is provided that is operable when enabled to
change the address stored by the storage means and including
enabling means for enabling the toggle gating means in response to
a control signal communicated over the
15. A code communication system according to claim 14 wherein means
is provided for rendering the toggle gating means effective to
change only the bit which was the last bit transmitted of the
address code transmitted during the next prior cycle of operation
of the system in said second
16. A code communication system according to claim 12 wherein
answer-back checking means is provided for checking an address code
received at a central station during a cycle against the address
code transmitted during that cycle and including means responsive
to the checking means for causing the station counting means to
repeat a cycle during roll call when the address code received is
out of correspondence with the address code
17. A code communication system according to claim 16 and including
means to limit the number of successive cycles during which the
same station
18. A code communication system according to claim 12 wherein the
mode selecting means is governed by signals communicated from the
remote stations over the communication channel for selectively
operating the system in said first mode if no start is registered
at one of the remote stations and for operating the system in said
second mode if a start is registered by communication of a signal
over the communication channel
19. A code communication system according to claim 18 wherein means
is provided for communicating a manifestation from a remote station
having registered a start when the system is operating in said
second mode and a bit of the address code received at that station
is out of correspondence with an address assigned to that station,
whereby the sensing of this manifestation at the central station
resets the communication apparatus at an intermediate point in a
cycle to initiate a new cycle of operation.
Description
While the invention is subject to a wide range of applications, it
is especially suited for use in a supervisory code communication
system and will be particularly described in that connection.
Code communication systems of this nature generally provide for
code communication between a plurality of remote stations and a
central station. Such a system can operate in first and second
modes wherein the mode 1 interrogates the remote stations from the
central stations in the roll call manner. In response to a change
in the condition of apparatus at one of the remote stations, the
system can be shifted into mode 2 wherein the station having a
change will communicate information to the central station. Mode 1
is for supervisory purposes to check periodically that each remote
station is operable, while the operation of the system in mode 2 is
to convey information to an abnormal nature such as an alarm
condition to the central office.
Prior art systems of this nature generally involve considerable
delay in switching from mode 1 to mode 2 because the roll call
continues in its usual operation of interrogating stations
successively after a change has taken place at a station until the
station having the change is interrogated.
An object of the present invention is to provide a code
communication system that substantially obviates one or more of the
limitations an disadvantages of the described prior art
systems.
Another object of the present invention is to provide a code
communication system having an improved system for locating a
station according to code superiority.
Another object of the present invention is to provide an improved
communication system of the roll call type providing for
communication of a limited number of repeat cycles in case of
communication error.
Another object of the present invention is to provide an improved
communication system providing selection of address codes in
accordance with different modes of operation of the code
communication system.
SUMMARY OF INVENTION
A code communication system is provided including at least one
communication channel for interrogating remote stations from a
central station during a communication cycle in response to a start
pulse communicated to the central station from one of the remote
stations. A transmitter at the central station is rendered operable
in response to a start pulse communicated from a remote station for
transmitting over the communication channel from the central office
a most superior search or station address code. The search code
thus transmitted is received at all remote stations and compared
with the code belonging to such station. Cycle reset means,
governed by a remote station having initiated a cycle by a start
pulse, is provided for causing the communication system to be reset
to start a new communication cycle upon reception at that remote
station of an address bit in the search code being transmitted from
the central station that disagrees with a station code assigned to
that station. The central station is responsive to the cycle reset
control for activating its transmitter to transmit another cycle
including the same address code as for the next prior cycle except
that the sense of the element is changed for the last bit
transmitted during such prior cycle.
The system is also operable in a roll call mode wherein means is
provided at the central station for checking integrity of reply
codes received during each roll call cycle. Means is provided for
comparing an address code transmitted from the central station
during each roll call cycle with an address code received at the
central station from a remote station and for delivering a trouble
output signal when the addresses compared are out of
correspondence. The roll call system provides for the transmission
of distinctive address codes during successive roll call cycles
from the central station to the remote station except that a repeat
cycle is transmitted to the same address in response to a trouble
output signal generated by the comparison of addresses.
The code communication system according to the present invention is
alternately operable in roll call and address search modes wherein
means is provided at the central station for selecting station
address codes for transmission over a communication channel to a
plurality of remote stations. A digital storage register is
provided at the central station for storing an address code for
transmission to the remote stations. A station counter is provided
for counting roll call cycles of operation and is operable when
enabled to deliver digital outputs to the storage register for
transmission to the remote stations in accordance with the station
count accumulated. Provision is also made for setting the address
storage register to a most superior address code for transmission,
and a mode selector is provided that is operable in first and
second modes for alternately enabling the station counter and the
code setting apparatus respectively to govern the address code
stored by the code storage register.
For a better understanding of the present invention, together with
other and further objects thereof, reference is had to the
following description, taken in connection with the accompanying
drawings, while its scope will be pointed out in the appending
claims.
FIGS. 1A and 1B when placed side-by-side illustrate a code
communication system provided according to one embodiment of the
present invention.
FIG. 2 illustrates more in detail part of the apparatus at a
central station illustrated in FIG. 1A.
GENERAL MODE OF OPERATION
With reference to FIGS. 1A and 1B, control and response
communication channels 30 and 31 are provided for connecting the
central station illustrated in FIG. 1A with a plurality of remote
stations such as stations No. 1 and No. 2 of FIG. 1B. Each of the
remote stations such as station No. 1 has a pulse transmitter 32
that is operable to transmit a start pulse over the response
channel 31 in response to a change in conditions at field station
No. 1. A receiver 33 is provided at the central station for
receiving the start pulse. The reception of the start pulse at the
central station enables a transmitter 34 to transmit a selected
most superior address code over the control channel 30 to the
remote stations. Each of the remote stations has a receiver 35 for
receiving addresses and control pulses communicated over the
control channel 30 from the central station. Each of the remote
stations also has apparatus including coincidence check circuits 36
which detect when the address code being received is out of
correspondence with the address assigned to the associated station.
When an out of correspondence condition is detected at a station
having transmitted a start pulse, the start pulse is removed from
the response channel by control of the pulse transmitter 32, and
this is effective at the central station through receiver 33 and
toggle AND gates 37 to reset the transmitting apparatus at the
central station and thus condition the system to initiate a new
cycle of operation. When this resetting takes place, the toggle AND
gates 37 are effective to change the character of the last address
bit that has been transmitted in an address and data register 38 so
that the opposite character for this bit will be transmitted as a
part of the address code during the next following cycle.
With reference to FIG. 2, the system has means for comparing an
answer-back address code in a register 39 with an address code that
was transmitted during the first part of the cycle and is stored in
register 38. This comparison is made by AND gates 41 and OR gate
42. Integrity check logic 43 delivers an output that is a data good
signal on wire 44 if the answer-back code corresponds, and such
output is effective to advance a station counter 45 to select a new
address code for the next roll call cycle. If, on the other hand,
the integrity check logic 43 detects an out of correspondence
condition, an output is applied by integrity check 43 on the
trouble wire 46 which does not advance the station counter on the
first cycle where trouble is detected, and thus causes the station
counter 45 to maintain its last stored address for the transmission
of a repeat cycle.
With reference to FIG. 1A, the code communication system according
to the present invention is operable alternately in roll call and
superiority address search modes in accordance with station
addresses stored in the address and data register 38. The address
code stored in address and data register 38 is obtained when the
system is in a roll call mode from station counter 45 which is
operable when enabled to deliver digital outputs to the address and
data register 38. When the system is in a superiority code address
mode, code setting apparatus including a one-shot gate 47 is
effective over wire 48 to govern the code stored in address and
data register 38. A mode selector 49 is operable in first and
second modes for alternately enabling the station counter 45 and
the code setting one-shot gate 47 respectively to govern the
address code stored in the address and data register 38.
The code communication system also has means including a dual bit
detector 125 (see FIGS. 1A and 2) for detecting when two or more
remote stations are responding at the same time so that they are
transmitting different characters for the same bit during a cycle
of operation. If such a condition is detected, an output of the
detector 125 is applied through integrity check logic 43 to trouble
wire 46 so as to provide the same mode of operation in case of
trouble detection as has been heretofore described.
Mode 1 Operation
In mode 1, the central station addresses the remote stations over
control channel 30 in accordance with a digital address code in the
station counter 45 (see FIG. 1A). The station counter 45 is never
reset, and is advanced one count at the end of each cycle of
operation, except when the integrity check logic 43 has determined
an error in the communication with a remote station. Under these
conditions, the transmission is repeated once to the same station.
If the trouble still exists, the counter 45 is advanced out count,
and a visual display is provided to indicate to an operator that
trouble has been encountered. Transfer of address codes from the
counter 45 to the address and data register 38 is rendered
effective by transfer gates 50 in accordance with a mode 1 enable
signal on wire 51 generated by mode selector 49 at the end of each
cycle. The address and data register 38 provides multiple readout
for inputs to a multiplexer 52. The multiplexer 52 comprises gates
for delivery selectively 1 or 0 series outputs on wires 53 and 54,
respectively, for governing the application of pulses by
transmitter 34 to the control channel 30 for transmission of a code
serially over the communication channel to the remote stations. The
multiplexer 52 includes gates that are enabled successively by
outputs of a counter 55, driven by a clock 56.
According to this embodiment of the present invention, the station
address counter 45 is a 10 bit counter, and the address and data
register 38 is a 16 bit register, the first 10 bits being provided
for the address code, and the remaining bits being provided for
data. Thus, the counter 55 is a 4 bit, 16 count binary counter, and
after having completed its count of 16, starts to count another
sequence of 16 counts. When the counter 55 has operated to a count
of 12, an output is enabled of gate 12 to set 12 detector latch 57.
This in turn delivers an output to AND gate 26, but output of the
AND gate 26 will not be enabled until the counter has operated
through its complete count and to a count of 10 in the next series
of counts so as to enable gate 10 to deliver an output on wire 59
to gate 26. Thus the cycle length is determined by a count of 26
pulses from the clock 56.
Output of gate 26 causes a reset pulse to be generated by the
one-shot 60, and output of the one-shot 60 is provided to a reset
pulse transmitter 61 for transmission of a reset pulse over a reset
channel 124 to reset all of the remote stations. At the same time,
reset energy is applied over wire 62 to reset apparatus 63 for
resetting the bit counter and registers. The reset pulse is also
applied over wire 64 to a pulse stretcher 65 for application as a
trigger pulse to the mode selector 49 over line 66. The mode
selector 49 remains in its mode 1 enable condition unless a start
pulse is received at this time over line 67 from the receiver 33.
If the integrity check logic 43 has determined the data is good, an
output is provided on wire 44 at this time, AND gate 68 is enabled
and the station counter 45 is advanced a count through OR gate
69.
With reference to FIG. 1B, pulses transmitted during a cycle from
the central station over control channel 30 are received at each
remote station by a receiver 35, and outputs for 1 and 0 characters
are provided on wires 70 and 71 respectively. An output on either
of these wires is effective through an OR gate 72 to operate a
counter 73 corresponding to the counter 55 at the central station.
Thus this counter 73 is actuated by pulses received over the
communication channel as clock pulses, irrespective of the
character of the bits. The counter 73 in turn governs the gates of
a multiplexer 74 that operates similar to the multiplexer 52
described for the central station. The station code to which the
respective remote stations are responsive is selected by a station
address code selector 75 which is conditioned for each station to
store a distinctive address code to which that station is
responsive. A 1 or 0 output is provided by the multiplexer for each
bit of the address code in correspondence with the code stored in
the address code selector 75 for the associated station, such code
being applied over line 76 to coincidence check circuit 36. This is
compared with bit by bit the 1 or 0 character that is received and
delivered to the coincidence check circuit over lines 77 and 78
respectively.
If there should be an out of correspondence condition in the
checking of the address codes, an output is delivered by the
coincidence check 36 over line 79 to anti-coincidence latch 80 so
as to set this latch. The setting of the anti-coincidence latch 80
provides an output over line 81 through an OR gate 82 to reset the
counter 73 over line 93 and maintain such counter in its reset
position as long as the anti-coincidence latch 80 is in its set
position. This latch is not reset until the reception of a reset
pulse from the central station at the end of the cycle.
This is the mode of operation that takes place at each of the
remote stations whose address does not correspond with the address
communicated during the roll call cycle from the central station.
At the end of the cycle, a reset pulse is received over the reset
channel 124 from the central office and applied through reset pulse
receiver 83 and over line 84 to the reset terminal R of the
anticoincidence latch 80. The resetting of the anti-coincidence
latch 80 conditions the counter 73 so that it can be responsive to
the pulses of the next cycle of operation of the communication
system.
To consider the mode of operation for a station that is called
during the roll call mode of operation, it will be assumed that the
remote station No. 1 shown in FIG. 1B is the station being
addressed during roll call transmission when the system is in
operation according to mode 1. Inasmuch as the entire ten bits of
the station address code under these conditions will correspond
with the code selected by the station address code selector 75, the
anti-coincidence latch 80 will not be set during the address code,
and thus the transmission will progress until the address code is
completed. According to the mode of operation as has been
heretofore considered, it will be noted that the receiving
apparatus at each remote station is permitted to continue to count
through the entire address code only provided there is no out of
correspondence condition. Thus when ten counts have been counted by
the counter 73 without the counter 73 having been reset, the
station has been selected, and an output is provided through AND
gate 85 which is responsive to the count of ten to set a transmit
latch 86 for enabling transmission of data from remote station No.
1 to the central station over response channel 31. At this time,
energy is removed from line 105 connecting the transmit latch with
the coincidence check circuits 36 to render the coincidence check
36 ineffective to set the anti-coincidence latch 80 in response to
an out of correspondence condition during transmission of data
bits.
The counter 73 continues to count in response to drive pulses that
are received over the control channel 30. Inputs to the
multi-plexer 74 for counts 11 through 16 are used to drive the
multiplexer to transmit monitoring code data as selected by control
devices and monitor code selector 87. The multi-plexer 74 thus
delivers 1 characters selectively for the data bits over lines 76
and 88 to a gate 89 that is enabled for the transmission of 1's and
0's in accordance with an input from the transmit latch over line
90. Transmit latch 86 enables an output of OR gate 91 over line 92
as an enable input to the pulse transmitter 32 for transmission of
1's and 0's as selected for the respective data pulses over the
response channel 31 to the central station.
Counter 73 is like the counter 55 at the central station in that it
counts to 16 and then starts counting over again so that when all
of the data pulses have been transmitted the system then proceeds
to repeat the address of remote station No. 1 into the response
channel 31 for verification at the central station. The central
station is thus repeating its station code, and in that the
transmit latch 86 at remote station No. 1 is in its set condition,
the multiplexer provides outputs to pulse transmitter 32 to
transmit the address code for station No. 1 to the central station.
At the end of the address thus transmitted, the central station
terminates the cycle by transmitting a reset pulse over the reset
channel 124 after the count of 26 as has been heretofore
considered, and such reset pulse is received by reset pulse
receiver 83 at remote station No. 1 and applied over line 84 to
reset the transmit latch 86 and to reset the counter 73 through OR
gate 82 over line 93.
Mode 2 Operation
It will now be considered that a change in status has become
effective at one of the devices 87 in FIG. 1B, and energy is
accordingly applied over line 94 to a status change detector 95
which in turn delivers an output over line 96 to set a change latch
97. The setting of latch 97 applies an output over line 98 to an
AND gate 99 so that such gate is enabled when the anti-coincidence
latch 80 is in its reset position, thus delivering an output over
line 101. Gate 99 when thus enabled delivers an output over line
101, through OR gate 91 and over line 92 to cause application of
energy continuously on the response channel 31. This energy is
decoded as a 0 by receiver 33 since gate 89 is de-energized. This 0
signal is the start pulse energy which has been heretofore
described.
With reference to FIG. 1A, the reception at the central station of
the start signal is applied over line 102 through receiver 33 to
line 67, and thus to mode selector 49. The mode selector 49 becomes
triggered to change from mode 1 to mode 2 enable in response to
energization of line 66 by pulse stretcher 65 upon generation of a
reset pulse at the end of a cycle of operation that may be in
progress. The removal of energy from mode 1 enable line 51 stops
the station counter 45 and removes the enable energy from transfer
gates 50 for the duration of mode 2 operations.
Mode selector 49 now provides an output over line 103 to one-shot
47 to enable the one-shot to set all 1's in the address and data
register 38. This is considered a most superior station code, and
the system, in searching for the station or stations that have
registered a start, will give preference to the station having the
most superior address code. Thus, if the most superior station to
which the code of all 1's is assigned has registered a start, that
station will be given preference over all other stations that may
have registered simultaneous starts to transmit its information
because it will be addressed first in response to the start
energization applied to the response channel 31. A mode 2 cycle is
thus transmitted the same as has been described for mode 1, with
the characters selected by multiplexer 52 wherein the station code
is determined by the address code that has been set into address
and data register 38 as has been described for mode 2 operation.
During this cycle, therefore, the multiplexer 52 provides outputs
of all 1's as the transmission of the address progresses during the
cycle.
As long as there is a remote station having applied a start pulse
whose address corresponds with the address bits being transmitted
from the central station, the central station continues to transmit
address pulses of the character 1, however, when this character
disagrees with a bit of the station code assigned to the most
superior remote station having a registered start, energy is
removed at such remote station from the response channel 31, and
the central station senses this removal to restart the cycle and to
change the character in register 38 from a 1 to a 0 for the bit
that was out of correspondence.
With reference to FIG. 1B, as in a normal cycle, when an element of
the address code is out of correspondence with the code assigned to
a station, the anti-coincidence latch 80 becomes set, and the
setting of this latch at a station having registered a status
change turns off the gate 99 by removing energy from the line 100.
This terminates the transmission of energy over the response
channel 31 to the central station, and the removal of such energy
removes energy from line 67 (see FIG. 1A) and thus from input to
the toggle AND gates 37 to cause an output of the toggle AND gate
37 on line 104 to provide an input to the one-shot 60 for
generating an output to reset the system for starting a new cycle
of operation. Resetting takes place at each of the remote stations
as has been heretofore considered at the end of a normal cycle.
Upon the reset pulse having reset the anti-coincidence latch 80
(see FIG. 1B) at station No. 1, energy is again applied to line 100
to enable the gate 99 to again deliver a start signal over response
channel 31 and thereby to maintain the mode selector 49 at the
central station in mode 2 for the next cycle of operation. Prior to
the termination of the prior cycle, the removal of energy from line
67 (see FIG. 1A) has become effective to actuate the toggle AND
gates 37 to change the character of the last address bit
transmitted from a 1 to a 0 for the cycle of operation now to be
started. Thus the system progresses in another cycle of operation
wherein at least one more address bit should be transmitted without
detection of an out of correspondence condition. If the balance of
the address code for the most superior station that has initiated a
start is all 1's, the station will be selected on this cycle, but
if the balance of the code is not all 1's for such station, the
system will restart the cycle and proceed in the same manner that
has been described to change the last code bit transmitted in the
address and to try again to locate the most superior station.
After selection of a station when the system is operating in mode
2, the system continues to operate the same as has been described
in mode 1 so as to transmit data from the remote station that has
been selected to the central station and to recheck the address as
has been heretofore described, thus completing a cycle having 26
bits of transmission. The transmission of the data from remote
station No. 1 (see FIG. 1B) is subsequent to the setting of the
transmit latch 86 as has been heretofore described, and at this
time energy is removed from line 105 connecting the transmit latch
with the coincidence check circuits 36 to render the coincidence
check 36 ineffective to set the anti-coincidence latch 80 in
response to an out of correspondence condition during transmission
of data parity bits. The output of AND gate 85, upon completing
reception of an address code at a remote station, resets the change
latch 97 over line 106 because of the selection of the associated
station having been successful to transmit data to the central
station. Because of the change latch 97 having been reset, there is
no energization at the end of the cycle of the response channel 31,
and accordingly at the central station the mode selector 49 is
changed to mode 1 enable and thus the system is restored to its
normal condition of roll call of the stations according to the
condition of station counter 45. Energy applied to the mode 1
enable line 51 enables gates 68 and 69 to step the station counter
45 for each cycle completed of the roll mode, and also energy
applied over line 51 enables transfer gates 50.
Integrity Check
With reference to FIG. 1A, code received from a remote station is
applied by receiver 33 over line 107 to address and data register
39. This register is shown more in detail in FIG. 2 as having 16
stages, 10 of which are used for address bits, and six of which are
used for data bits. The data bits are actually received before the
address bits, and thus if the register 39 is a shift register, the
bits are so circulated that the register 39 will be conditioned
with the bits in the same order as the order in which the bits are
stored in the register 38. Thus the registers 38 and 39 are
compared at the end of each cycle for corresponding address codes.
Results of the comparison are rendered effective to deliver data
good, or data not good, outputs in accordance with an enable signal
applied from the one-shot 60 at the end of the cycle.
AND gates 41 are provided for comparing the address code bits
selected for transmission with the address answer-back code bits,
bit for bit. These gates have outputs enabled only where there is
an out of correspondence condition in one of the address bits, and
in such case the output of a gate 41 is applied through OR gate 42
over line 108 to an AND gate 109 that is enabled at the end of the
cycle by output of one-shot 60 on line 110. An output of gate 109
is applied over line 111 through OR gate 112 over wire 113 to AND
gate 114. Energy of line 113 is also effective through an inverter
115 to set a trouble latch 116. This prevents enabling gate 114
over line 117 in order to permit the system to repeat a cycle to
the same station and perhaps obtain a valid code.
If the integrity check logic 43 determines during the next cycle
that the data is good, an output is provided on data good wire 44
through AND gate 118 and inverter 119 to add a count to station
counter 45 (see FIG. 1A) through AND gate 68 and OR gate 69. Also,
with reference to FIG. 2, the trouble latch 116 is reset by output
of gate 118. If there has been only one trouble cycle, there has
been no output of gate 114, because an output of this gate is
enabled only provided that there are two successive trouble cycles
detected. If there are two successive trouble cycles detected, the
second trouble cycle causes an output of gate 114 because the
trouble latch 116 is not reset, and thus an address storage 121 is
enabled to store the address of the station having the trouble, the
address being transferred from address and data storage 38. A
digital trouble indicator 122 is provided for indicating the
station number having the trouble, and an alarm 123 is actuated to
call the trouble condition to the attention of an operator at the
central station.
The apparatus that has been described for sensing and indicating
trouble because of lack of correspondence between the address code
transmitted and the address code received is also used to indicate
trouble because of dual bit detection. This detection is made by
the dual bit detector 125, an output of which is effective to
enable AND gate 128 to provide an input to OR gate 112 to render
effective the data good and data not good outputs which control the
trouble indication and transmission of a repeat cycle the same as
has been heretofore described by trouble sensed upon comparison of
address codes.
When it has been determined that the data is good by integrity
check logic 43 including comparator and dual bit detection gates
(see FIG. 1A), an output is applied over line 130 to a decoder 131.
The decoder 131 delivers outputs to Station No. 1 indicators 132
and Station No. 2 indicators 133 over lines 134 and 135
respectively.
The communication system is also adapted to transmit designated
controls from the central station to the remote station by
selecting data bits for transmission by the central station during
the period in the communication cycle when the address code is not
being transmitted by the central for comparison with the stored
code for each remote station. A control data selector 136 is
provided for this purpose. Its output governs address and data
register 38 over line 137.
Separate control, response and reset channels 30, 31 and 124 are
illustrated in the drawings for connecting the communication
apparatus at the central station with the communication apparatus
at the remote stations. With this organization, direct current PCM
codes can be used for communication. These can be of opposite
polarity for 1's and 0's respectively. It is to be understood,
however, that where conditions warrant the combining of the
channels over a single line circuit, carrier station frequency
communication may be employed wherein the central station would
transmit on distinctive frequencies as compared to the frequencies
used for the remote stations to respond.
While there has been described what is at present considered to be
the preferred embodiment of the invention, it will be obvious to
those skilled in the art that various changes and modifications may
be made therein without departing from the invention.
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