Rs422 Interface - GE T60 Instruction Manual

3.3 DIRECT INPUT/OUTPUT COMMUNICATIONS
a) DESCRIPTION
There are two RS422 inter-relay communications modules available: single-channel RS422 (module 7T) and dual-channel
RS422 (module 7W). The modules can be configured to run at 64 kbps or 128 kbps. AWG 20-24 twisted shielded pair cable
is recommended for external connections. These modules are protected by optically-isolated surge suppression devices.
The shield pins (6a and 7b) are internally connected to the ground pin (8a). Proper shield termination is as follows:
• Site 1: Terminate shield to pins 6a or 7b or both.
• Site 2: Terminate shield to COM pin 2b.
Match the clock terminating impedance with the impedance of the line.
3
The following figure shows the typical pin interconnection between two single-channel RS422 interfaces installed in slot W.
All pin interconnections are to be maintained for a connection to a multiplexer.
Figure 3–37: TYPICAL PIN INTERCONNECTION BETWEEN TWO RS422 INTERFACES
b) TWO-CHANNEL APPLICATION VIA MULTIPLEXERS
The RS422 interface can be used for single channel or two channel applications over SONET/SDH or multiplexed systems.
When used in single-channel applications, the RS422 interface links to higher order systems in a typical fashion observing
transmit (Tx), receive (Rx), and send timing (ST) connections. However, when used in two-channel applications, certain cri-
teria must be followed since there is one clock input for the two RS422 channels. The system functions correctly when the
following connections are observed and your data module has a terminal timing feature. Terminal timing is a common fea-
ture to most synchronous data units that allows the module to accept timing from an external source. Using the terminal
timing feature, two channel applications can be achieved if these connections are followed: The send timing outputs from
the multiplexer (data module 1), connects to the clock inputs of the UR–RS422 interface in the usual fashion. In addition,
the send timing outputs of data module 1 is also paralleled to the terminal timing inputs of data module 2. By using this con-
figuration, the timing for both data modules and both UR–RS422 channels are derived from a single clock source. As a
result, data sampling for both of the UR–RS422 channels is synchronized via the send timing leads on data module 1 as
shown below. If the terminal timing feature is not available or this type of connection is not desired, the G.703 interface is a
viable option that does not impose timing restrictions.
3-32
Single-channel RS422 module
~ 3b
Tx –
~ 3a
Rx –
~ 2a
RS422
Tx +
~ 4b
Rx +
6a
~
Shield
7a
~
Clock
8b
~
~ 2b COM
Surge
~ 8a
~ indicates the slot position
Figure 3–36: RS422 INTERFACE CONNECTIONS
T60 Transformer Protection System
Dual-channel RS422 module
~ 3b
Tx –
~ 3a
Rx –
RS422
~ 2a
Tx +
channel 1
~ 4b
Rx +
6a
~
Shield
5b
~
Tx –
5a
~
Rx –
RS422
~ 4a
Tx +
channel 2
~ 6b
Rx +
~ 7b
Shield
~ 7a
Clock
~ 8b
~ 2b
COM
~ 8a Surge
842776A3.CDR
3 HARDWARE

3.3.5 RS422 INTERFACE

GE Multilin