CHAPTER 3: INSTALLATION PILOT CHANNEL COMMUNICATIONSL30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 3-373criteria must be followed since there is one clock input for the two RS422 channels. The system functions correctly whenthe following connections are observed and your data module has a terminal timing feature. Terminal timing is a commonfeature to most synchronous data units that allows the module to accept timing from an external source. Using theterminal timing feature, two-channel applications can be achieved if these connections are followed: the send timingoutputs from the multiplexer (data module 1) connects to the clock inputs of the UR RS422 interface in the usual way. Inaddition, the send timing outputs of data module 1 are also paralleled to the terminal timing inputs of data module 2. Byusing this configuration, the timing for both data modules and both UR RS422 channels are derived from a single clocksource. As a result, data sampling for both of the UR RS422 channels is synchronized via the send timing leads on datamodule 1, shown as follows. If the terminal timing feature is not available or this type of connection is not wanted, theG.703 interface is a viable option that does not impose timing restrictions.Figure 3-39: Timing configuration for RS422 two-channel, three-terminal applicationData module 1 provides timing to the L30 RS422 interface via the ST(A) and ST(B) outputs. Data module 1 also providestiming to data module 2 TT(A) and TT(B) inputs via the ST(A) and AT(B) outputs. The data module pin numbers have beenomitted in the figure because they vary by manufacturer.
