CHAPTER 3: INSTALLATION PILOT CHANNEL COMMUNICATIONSL30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 3-3933.4.4 RS422 interface3.4.4.1 DescriptionThere are three RS422 inter-relay communications modules available: single-channel RS422 (module 7T), dual-channelRS422 (module 7W), and dual-channel dual-clock RS422 (module 7V). The modules can be configured to run at 64 or128 kbps. AWG 24 twisted shielded pair cable is recommended for external connections. These modules are protected byoptically-isolated surge suppression devices.The shield pins (6a and 7b) are connected internally 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 2bMatch the clock terminating impedance with the impedance of the line.Figure 3-40: RS422 interface connectionsThe 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 3-41: Typical pin interconnection between two RS422 interfaces3.4.4.2 Two-channel application via multiplexersThe 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 way, observingtransmit (Tx), receive (Rx), and send timing (ST) connections. However, when used in two-channel applications, certainThe two-channel two-clock RS422 interface (module 7V) is intended for use with two independent channel bankswith two independent clocks. It is intended for situations where a single clock for both channels is not acceptable.
