SERIES IP521 INDUSTRIAL I/O PACK EIA/TIA-422B SERIAL COMMUNICATION MODULE
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RxD
1. FOR AN RS422 NETWORK, INSTALL A TERMINATING RESISTOR AT THE
RECEIVING END OF THE NETWORK ONLY
NOTES CONCERNING RESISTOR PLACEMENT AND REMOVAL FOR RT AND RB:
UNIT I
(DCE)
TxD_ENABLE
4. THE TxD LINE SOURCED FROM A PORT CAN BE PERMANENTLY ENABLED
VIA SOFTWARE. IF SO, THE NETWORK BIAS RESISTORS ASSOCIATED WITH
EACH PAIR OF SIGNAL WIRES WILL NOT BE NEEDED. THESE RESISTORS
ARE INSTALLED IN SOCKETS AND CAN BE REMOVED IF THESE DRIVERS ARE
ALWAYS ENABLED.
3. THERE MUST BE AT MOST, ONE SET OF BIAS RESISTORS ASSOCIATED
WITH EACH PAIR OF SIGNAL WIRES TO KEEP THE NETWORK FROM
FLOATING WHEN NO UNITS ARE TRANSMITTING.
2. ALL RS422/RS485 TRANSMITTING AND RECEIVING CHANNELS MAY HAVE
TERMINATING RESISTORS (RT) AT BOTH ENDS OF THE NETWORK. THE
IP521 HAS THESE RESISTORS (120 OHM) INSTALLED IN SOCKETS AND THEY
MAY BE REMOVED AS REQUIRED.
RT
RxD-
TxD
RxD_ENABLE
RxD
TxD+
TxD-
RxD+
RxD-
IP521 RS-422/485 INTERFACE DIAGRAM
UNIT 1 (DTE)
UNIT 1 (DTE)
RxD_ENABLE
TxD_ENABLE
TxD
RB
-VB
RxD+
TxD-
TxD+
RB
+VB
RS422/RS485 FULL DUPLEX (MULTIDROP NETWORK)
RT
TxD
TxD_ENABLE
RxD_ENABLE
RxD
RxD-
RxD+
TxD-
TxD+
+VB
RS422 FULL DUPLEX (TWO NODE NETWORK)
RB
-VB
RB
TxD+
RT
RT
TxD-
RB
RxD+
-VB
RB
TxD_ENABLE
TxD
RxD_ENABLE
+VB
RxD
RxD-
RT
RxD+
TxD-
TxD+
RB
RxD
RxD_ENABLE
TxD
+VB
UNIT 2 (DCE)
UNIT N (DCE)
RB
RxD-
TxD_ENABLE
-VB
5. THE IDLE STATE OF THE TxD & RxD DATA PAIRS ARE HIGH ON TxD+
& RxD+. THIS CORRESPONDS TO A MARK (1) ON THE DATA LINE.
6. RS-422 IS CONSIDERED A BALANCED (DIFFERENTIAL) TRANSMISSION
STANDARD BECAUSE THE VOLTAGE OF ONE SIGNAL LINE IS TAKEN
WITH RESPECT TO ANOTHER TO DETERMINE THE SIGNAL LEVEL.
4501-714A
