Communication module

A loop circuit interface module enabling a plurality of data terminals remote from each other and from a central controller to communicate with each other and the central controller over a plurality of data channels interconnecting same is disclosed. The loop circuit interface module comprises a plurality of data ports for inputting data from either the loop controller or another loop circuit interface module. The data ports also output data to the loop controller or another loop circuit interface module. The module has a plurality of signal ports for inputting data from the data terminal and for outputting data to the data terminal. A bridging means provides a matched impedance between the loop circuit interface module, the loop controller, and the data terminals. The bridging further provides gain to the data at the plurality of ports. Switching means selectively and controllable connects the plurality of data ports and the plurality of signal ports directly to each other, or to each other through the bridging means.

FIELD OF THE INVENTION 
The present invention relates in general to data communication systems, and 
more particularly, to communication modules for use in loop type data 
communication systems. 
BACKGROUND ART 
Communicating data or other information between a central location and 
remotely located data terminals, such as automatic bank teller machines or 
the like, using conventional telephone lines or data channels is old in 
the art. A configuration used to provide such communication capability 
utilizes serially connected unidirectional or simplex data channels 
between each remotely located data terminal. The first and last data 
terminals were subsequently connected to the central location to form a 
serial, closed loop communication system. The success of this 
configuration require the continued serial operation of a number of 
components; including, each data channel, each remote terminal, and the 
electronic circuitry at each termination of the data channel used to 
modulate and demodulate the data on the data channel. A failure of any one 
of these components rendered the entire configuration inoperable. Because 
remote terminals may be widely distributed within a particular location, 
as for example, at different geographical locations within a city, the 
common carrier providing the simplex data channels may regard each remote 
data terminal as a separate and independent data circuit. As such, 
remedial service for this serial configuration may be provided by numerous 
field personnel from the common carrier based at the geographic location 
of each remote data terminal. Thus, a configuration with N data terminals 
may require N different service locations to isolate a failure to a 
particular data channel or a particular remote data terminal, or to 
satisfactorily demonstrate that all data channels are operating correctly. 
Regardless of a common carrier's ability or inability to provide field 
service personnel to identify and resolve problems, a significant 
disadvantage of this serial, closed loop configuration is the lack of a 
central point from which all data channels emanate, or to which all data 
channels arrive. A simple continuity test verifying the integrity of the 
closed loop configuration becomes virtually impossible to perform from a 
single central location. Thus, fault identification and isolation becomes 
slow and cumbersome, and restoration of the communication configuration 
must await identification and repair of all the failed components. 
Another configuration solving the problems of the aforementioned serial, 
closed loop configuration interconnected each remote data terminal to the 
central location with a bidirectional or duplex data channel. Adjacent 
remote data terminals were interconnected to each other essentially by 
interconnecting the transmit and receive portions of adjacent data 
channels. However, interconnecting adjacent remote data terminals cannot 
be accomplished by simply interconnecting the transmit and receive 
portions of adjacent duplex data channels. This is partially due to the 
fact that the remote data channels provided by the common carrier 
attenuate the data propagated along the data channel. In addition, an 
impedance mismatch may occur between the remote data terminal internal 
electronics and the characteristic impedance of the data channel making 
such a direct interconnection virtually impossible. To more effectively 
utilize the duplex configuration, an active and sophisticated device or 
communication module must provide the interface between adjacent remote 
data terminals, the data channels, and the central location. 
The present invention provides such a communication module. By having a 
plurality of data and signal ports, the present invention provides the 
requisite interfaces for both the remote data terminal and a loop 
controller within the central location. Circuitry within the module 
ensures the data propogated along the data channel interfaces with either 
an associated data terminal, another communication module, or the loop 
controller. A switching means provides a capability to easily and quickly 
switch around a failed component so that data communications with other 
remote data terminals may be continued. Finally, means within the present 
invention provides a capability to identify the location within the duplex 
loop configuration at which point a failure has occurred. 
Sarle, U.S. Pat. No. 4,035,770 discloses, in part, a switching system for 
use with a plurality of data terminals connected in series in a loop. The 
disclosed system does not regenerate the data communicated for subsequent 
transmission to another data terminal, or another like system, nor does 
the reference provide a diagnostic capability to identify the point and 
component at which a loop failure has occurred. The patent to Hackett, 
U.S. Pat. No. 3,958,111 discloses a commandable diagnostic controller to 
autonomously simulate data received over an out-of-service data path. The 
disclosed system provides for a remote device which interfaces redundant 
data paths, and performs and reports a number of remote tests of digital 
switching apparatus along one of those data paths. The disclosed system 
does not provide for the transmission of information, nor does the 
reference detect impairment in the data channel or provide means for 
testing the data channel itself. 
SUMMARY OF THE INVENTION 
According to one aspect of the present invention, the loop circuit 
interface module enabling a plurality of data terminals remote from each 
other and from a central controller to communicate with each other and the 
central controller over a plurality of data channels interconnecting same 
comprises a plurality of data ports. The data ports input data from either 
the loop controller or another loop circuit interface module, and output 
data to the loop controller or another loop circuit interface module. A 
plurality of signal ports inputs data from the data terminal and outputs 
data to the data terminal. Bridging means provides a matched impedance 
between the loop circuit interface module, the loop controller, and the 
remote data terminals. The bridging means further provides gain to the 
data on either plurality of ports. Switching means selectively and 
controllably connects the plurality of data ports and the plurality of 
signal ports directly to each other, or to each other through the bridging 
means. 
An object of the present invention is to provide a communication module 
enabling a plurality of remote data terminals to communicate with each 
other and with a central controller over a communication data loop 
interconnecting same. 
A further object of the present invention is to provide a communication 
module enabling a plurality of remote data terminals and a central 
controller to communicate with each other in the presence of a failure in 
a remote data terminal by providing a data path around the failed data 
terminal. 
A still further object of the present invention is to provide a 
communication module having a capability to identify the point in a loop 
type communication system at which a failure has occurred. 
A still further object of the present invention is to provide a 
standardized communication module replaceable with like communication 
modules used in any loop type communication systems. 
A still further object of the present invention is to provide a 
communication module compatible with a common carrier supplied data 
channel. 
These and other objects, features, and advantages of the present invention 
will become more apparent in light of the detailed description of the 
preferred embodiment set forth hereafter, and illustrated in the 
accompanying drawings.

BEST MODE OF CARRYING OUT THE PRESENT INVENTION 
With reference to FIGS. 1-3, the loop circuit interface module of the 
present invention, shown generally at 10, comprises a plurality of data 
ports 20 for inputting data from either a loop controller 12 or another 
loop circuit interface module. The loop controller generally consists of 
electronic circuitry within the central controller 14 and provides the 
interface between the central controller and the present invention. The 
loop controller and the central control are not part of the present 
invention. The plurality of ports 20 also enable the outputting of data to 
the loop controller or another loop circuit interface module. A plurality 
of signal ports 22 inputs data from a remote data terminal 16 and outputs 
data to the remote data terminal. Bridging means, shown at 30, provides a 
matched impedance between the loop circuit interface module of the present 
invention, the loop controller, and each of the plurality of remote data 
terminals. The bridging means further provides gain to the data on each of 
the plurality of ports 20, 22. Switching means 40 selectively and 
controllably connects the plurality of data ports 20 and the plurality of 
signal ports 22 directly to each other, or to each other through the 
bridging means 30. A detector and actuation means 50 enables the loop 
circuit interface module to detect the presence or absence of data 
activity at either plurality of ports 20, 22, and is further operable to 
output a code in response to the absence of data activity at either 
plurality of ports. Each of these elements, together with other elements 
comprising the present invention will next be described in more detail 
below. 
With reference to FIG. 2, a plurality of loop circuit interface modules 
according to the present invention are shown configured to communicate 
with a plurality of remote data terminals 16 and a loop controller 12 
within the central controller 14. In this configuration, each loop circuit 
interface module physically is located within the central controller while 
the plurality of remote data terminals are remote from each other and the 
central controller. Each remote data terminal is connected to the central 
controller and a loop circuit interface module through a plurality of 
bidirectional or duplex data channels 18 disposed therebetween. The duplex 
data channels are typically provided by a common carrier, such as American 
Telephone and Telegraph or some other private utility-type company. Each 
data channel is electrically terminated at its ends by common carrier or 
by customer provided modulator-demodulators converting the data signals 
appearing on the data channel into digital signals available for 
subsequent use by either the data terminals or the central controller. 
In the configuration as shown, communication data is routed by the central 
controller to a data port 20 of one loop circuit interface module. The 
data routed to the module is typically in frequency shift keyed binary 
form having a power level of substantially 0 dBm. The switch means 40 
internal to the module is manually operable by a plurality of switches on 
each module (see FIG. 4) to route this data through the bridging means 30 
and the output impedance circuit 34 to one of the plurality of signal 
ports 22 for subsequent transmission to a data terminal 16 remote from the 
central controller. An input impedance circuit 31 within the bridging 
means is operable to provide a requisite impedance match between the loop 
controller and the module. In the preferred embodiment, the impedance 
circuit provides a substantially six hundred ohm load to the loop 
controller. A gain insertion circuit 32, also a portion of the bridging 
means, provides a substantially 16 dB gain to the data before it is 
subsequently switched to the signal port 22. The gain is needed since each 
common carrier provided data channel has a typical power loss of 16 dB 
along its length. The output impedance circuit 34 ensures the output 
impedance of the loop circuit interface module matches the characteristic 
impedance of the data channel. 
Data received from a data terminal 16, also in a frequency shift keyed 
analong form, is applied to one of the plurality of signal ports 22. The 
switching means 30 is manually operable to route this data either directly 
to another module or to the loop controller. If the data is routed to 
another module, the process above is repeated until each data terminal in 
the loop has received communication data or has responded with data to the 
loop controller. It can be seen that in the configuration shown in FIG. 2, 
the present invention interfaces both the loop controller and the remote 
terminals without the need for additional expensive and complicated 
modulator-demodulators. 
As will be discussed more fully below, each loop circuit interface module 
includes a detector and actuation means 50 and a display means 60 for 
detecting the presence or absence of data activity at the plurality of 
ports 20, 22 and for displaying same. In the configuration shown in FIG. 
2, the detector and actuation means outputs a code in response to the 
absence of data activity occurring at signal port 22 after a predetermined 
period of time. The code is operable to control the illumination of a 
plurality of indicator lights (not shown) disposed on each module. By way 
of example, if the means 50 detects the presence of a frequency shift 
keyed binary one from the remote data terminal, typically at 2100 Hz, the 
output code illuminates a green indicator light indicating the remote data 
terminal is operational. If the means 50 does not detect the presence of a 
frequency shift keyed binary zero, typically 1300 Hz, for a period of five 
seconds, the output code illuminates a yellow indicator light which is an 
indication of a potential failure in either the loop module, the data 
channel, or the data terminal. The absence of either a binary one or 
binary zero detection for a period of five seconds illuminates a red 
indicator light indicating a failure in either the module, the data 
channel, or the remote data terminal. 
When a failure has occurred, the switching means is manually operable to 
switch the failed component out of the communication loop and enable 
continued communications between the loop controller and the remote data 
terminals. In this instance, the switching means is operable to connect 
the plurality of data ports 20 directly to each other while concurrently 
removing, via an open circuit, the plurality of signal ports 22 from 
electrical connection with the module. 
To ensure each loop circuit interface module in this configuration is 
replaceable with any other module, an attenuation module (not shown) 
providing a substantially 16 dB attenuation in the data routed to the 
first loop circuit interface module is disposed between the loop 
controller and the first module. In this manner, the first operable 
module, that is one that has not been switched so as to bypass a remote 
data terminal, provides substantially a 16 dB gain to the communication 
data prior to switching same to its associated remote data terminal. 
With reference to FIG. 3, an alternate configuration for connecting a 
plurality of loop circuit interface modules according to the present 
invention is to a central controller 14 and a plurality of remote data 
terminals 16 is shown. In this configuration, each loop circuit interface 
module is located in close proximity to each remote data terminal. The 
loop circuit interface module is connected to another loop circuit 
interface module or the central controller through a plurality of 
bidirectional or duplex data channels 18 disposed therebetween. As 
previously mentioned, each duplex data channel is typically provided by 
the common carrier and is electronically terminated at each end by a 
modulator-demodulator provided by either the common carrier or the 
customer. The communication data propogated along the data channel is 
typically of frequency shift keyed analog form with a binary one being 
typically represented by a 2100 Hz signal and a binary zero being 
represented by a 1300 Hz signal. 
If the loop circuit interface module and its associated remote data 
terminal are both operational, the switching means routes the data from 
the loop controller appearing at one of the plurality of data ports 20 to 
one of the plurality of signal ports 22 for subsequent use by the remote 
data terminal. The detector and actuation means 50 is switchably operable 
to monitor the presence or absence of data activity at the plurality of 
parts 20, while the bridging means 30 is switchably removed from effecting 
the communication data in this instance. Data from a remote data terminal 
appearing at one of the signal ports 22 is switched directly to one of the 
data ports 20 for subsequent transmission (via the modulator-demodulator 
at one end of the data channel) to another module or to the loop 
controller. 
If a loop circuit interface module or its associated remote data terminal 
is inoperative, the switching means in conjunction with the detector and 
actuation means is manually operable to switch the communication data on 
one of the plurality of data ports 20 through the bridging means 30 to 
another of the plurality of data ports. The plurality of signal ports 22 
are electronically removed by open circuit from electronic connection with 
the module. It can be seen that in this configuration, the present 
invention maintains continued communications between the loop controller, 
remote data terminals, and loop circuit interface modules without the use 
of additional modulator-demodulators. 
in the configuration shown in FIG. 3, the switching means 40 is either 
manually or automatically activated to effect the switching of the 
communication data between a data terminal, another module, and the loop 
controller as described. If manually switched, personnel at the data 
terminal are informed of the potential inoperability of a data terminal by 
the plurality of indicator lights on each module as has been described. If 
automatically activated, the module propogates a command frequency 
(typically 1700 Hz) issued at a test point between the loop controller and 
the first data channel interconnected by loop circuit modules. The command 
frequency triggers the automatic operation of the switching means. A 
consequence of the operation of the switching means is that the command 
frequency is propogated to other units, and ultimately back to the loop 
controller. Such a process provides for an end-to-end continuity test of a 
series of otherwise electrically and mechanically unconnected data 
channels. 
With reference to FIG. 4 and Table 1 below, the operation of a typical loop 
circuit interface module will next be described. The communication data 
from the loop controller or another module is typically in binary form and 
is typically input to the present invention at a 0 dBm signal level. The 
signal is first passed through an attenuator to the normal-bypass switch 
SW1. If the switch is in the normal mode, the signal is then passed 
through differential amplifier U1A. The input to the differential 
amplifier utilizes two three hundred ohm resistors, R74, R75 forming a 
balanced, input for the amplifier while maintaining a typical six hundred 
ohm input impedance for the module. Bypass capacitors C19, C20 isolate any 
DC signal appearing on the communication signal input while maintaining 
the bias signals required by amplifier U1A. The bias for the amplifier U1A 
is provided by the plurality of resistors R49, R50, R70, R71, R72, and 
R73. The gain of the differential amplifier can be varied by adjusting the 
value of resistor R73. The output of the amplifier stage is connected to 
the primary side of a coupling transformer T1. The secondary of the 
transformer is connected in parallel to a monitoring jack J1 and 
subsequently to a remote data terminal. The monitoring jack J1 permits the 
audio monitoring of the signal switched to the data terminal. 
Data received from a remote data terminal is switchable by SW1 directly to 
either another loop control interface module or the central controller. In 
this instance, the signal merely is routed directly by switch SW1 to these 
units (without amplification). In this instance, the signal will be 
substantially at a 16 dBm level. 
In the instance when a remote data terminal has failed or is otherwise 
rendered inoperable, the switch SW1 is manually switchable to the bypass 
position. In this manner, the communication data from the loop controller 
or another remote data module is switched directly to another data module 
or back to the loop controller. The plurality of monitor jacks J2 allow 
the monitoring of the data channel communication data without any 
interference from any other signals and the performance of testing on the 
data channel. An additional feature of the jacks is that in a normal 
operation it becomes possible to listen to the communication data on the 
data channels without interference to the communication data. 
The operation of the detector and actuation means will next be described. 
Communication data received from a remote data terminal, loop controller 
or another module is applied to a differential amplifier U1B operationally 
configured similarly to amplifier U1A described above. The output of 
amplifier U1B is routed through a blocking capacitor C21 to tone decoders 
U2 and &3 tuned typically to 2100 Hz and 1300 Hz respectively. Tuning for 
each is provided by resistors R78 and R80 respectively. When a 2100 Hz 
tone is detected, light emitting diode CR6 is biased on causing a green 
indicator to be lit. If a 2100 Hz tone is not detected, charging current 
provided by the detector U2 leaks through resistors R77, R83, and diode 
CR6 charging capacitor C32. A comparator U1D is thereafter biased into 
conduction causing light emitting diode CR 10 to conduct illuminating a 
red indicator light. This light indicates no received data. The conduction 
process takes approximately five seconds due to the charging of capacitor 
C32. A similar circuit is provided for the detection of a 1300 Hz tone. In 
the absence of a 1300 Hz tone transition for approximately four seconds, 
comparator U1C will cause light emitting diode CR9 to conduct illuminating 
a yellow indicator indicating the absence of normal 1300-2100 Hertz 
transitions. This condition signifies a constant 2100 Hertz tone, which is 
sent by loop terminals which are not receiving valid communication. 
TABLE 1 
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REFERENCE 
DESIGNATION DESCRIPTION 
______________________________________ 
R1, R2, R4, R6, R9, 
10K.OMEGA. 1/4w .+-. 5% Carbon 
R81, R84, R85, R87, 
R90 
R10, R3, R82, R83 
30K.OMEGA. 1/4w .+-. 5% Carbon 
R12, R5, R86, R89 
1K.OMEGA. 1/4w .+-. 5% Carbon 
R8, R7, R78, R80 
10K.OMEGA. Trimmer Potentiometer 
R13, R11, R76, R79 
4.7K.OMEGA. 1/4w .+-. 5% Carbon 
R14, R15, R17, R18 
100K.OMEGA. 1/4w .+-. 5% Carbon 
R19, R20, R23, R24 
R25, R26, R27, R28 
R42, R43, R44, R45 
R46, R47, R49, R50 
R60, R70, R71, R72 
R16, R29, R48, R73 
110K.OMEGA. 1/4w .+-. 5% Carbon 
R21, R22, R74, R75 
300.OMEGA. 1/4w .+-. 5% Carbon 
R30, R77 330.OMEGA. 1/4w .+-. 5% Carbon 
R40, R88 660.OMEGA. 1/4w .+-. 5% Carbon 
R41, R91 720.OMEGA. 1/4w .+-. 5% Carbon 
C1, C4, C31, C32 
100.mu.F 20V Electrolytic, Type 500 D 
C2, C3, C8, C12, 
0.1.mu.F 20V Capacitor 
C13, C14, C15, C16 
C17, C18, C19, C20 
C21, C22, C27, C30 
C5, C9, C25, C29 
2.2.mu.F 20V Dipped Tantalum, 
Type 196D Electrolytic 
C7, C10, C23, C26 
220.mu.F 20V Electrolytic, 
Type 500 D 
C11, C6, C24, C28 
1.mu.F 20V Electrolytic, Type 196 D 
CR1, CR4, CR7, CR8 
IN 914 Diode 
CR2, CR10 Red LED 
CR3, CR9 Yellow LED 
CR5, CR6 Green LED 
Q1, Q2 2N3904 
U1, U5, LM 324 Quad op amps 
U2, U3, U6, U7 LM 567 Tone Decoder 
J1, J2, J3, J4 Miniature Phone Jack, 
Switch Craft 142A 
SW1, SW2 4 pole double throw switch, 
toggle type bushing size 
.25 inches O.D. 
T1, T2 Telephone coupling transformers 
900.OMEGA. primary 600.OMEGA. 
secondary, Triad TY-301P 
CR1-4 Bridge Rectifier, PD20EDI7811 
C1 and C2 Capacitors-470 mF 50 Volt 
Electrolytic 
C3 and C4 100.mu.F 20 Volt Electrolytic 
Capacitor 
CR4-5-6 Red LED 
R1 and R2 330 .OMEGA. 1/4 watt 5% Carbon 
R3 4K 5Watt resistor-wire wound 
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