3-34 B30 Bus Differential System GE Multilin3.3 DIRECT INPUT AND OUTPUT COMMUNICATIONS 3 HARDWAREFigure 3–38: TIMING CONFIGURATION FOR RS422 TWO-CHANNEL, 3-TERMINAL APPLICATIONData module 1 provides timing to the B30 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 above since they vary by manufacturer.c) TRANSMIT TIMINGThe RS422 interface accepts one clock input for transmit timing. It is important that the rising edge of the 64 kHz transmittiming clock of the multiplexer interface is sampling the data in the center of the transmit data window. Therefore, it is impor-tant to confirm clock and data transitions to ensure proper system operation. For example, the following figure shows thepositive edge of the Tx clock in the center of the Tx data bit.Figure 3–39: CLOCK AND DATA TRANSITIONSd) RECEIVE TIMINGThe RS422 interface utilizes NRZI-MARK modulation code and; therefore, does not rely on an Rx clock to recapture data.NRZI-MARK is an edge-type, invertible, self-clocking code.Data module 1Data module 2Signal nameSignal nameSD(A) - Send dataTT(A) - Terminal timingTT(B) - Terminal timingSD(B) - Send dataRD(A) - Received dataRD(A) - Received dataSD(A) - Send dataSD(B) - Send dataRD(B) - Received dataRD(B) - Received dataRS(A) - Request to send (RTS)RS(A) - Request to send (RTS)RT(A) - Receive timingCS(A) - Clear To sendCS(A) - Clear To sendRT(B) - Receive timingCS(B) - Clear To sendCS(B) - Clear To sendLocal loopbackLocal loopbackRemote loopbackRemote loopbackSignal groundSignal groundST(A) - Send timingST(A) - Send timingST(B) - Send timingST(B) - Send timingRS(B) - Request to send (RTS)RS(B) - Request to send (RTS)831022A3.CDRW 7aW 2bW 8a7WShld.Shld.Tx1(+)Tx2(+)Tx1(-)Tx2(-)Rx1(+)Rx2(+)+comRx1(-)Rx2(-)–INTER-RELAY COMMUNICATIONSW 3aW 5bW 5aW 3bW 2aW 6aW 6bW 7bW 8bW 4bW 4aRS422CHANNEL 1RS422CHANNEL 2CLOCKSURGETx ClockTx Data
