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ROC800-Series Instruction Manual
Revised Jul-14
Communications
5-11
used to multi-drop units on a serial network over long distances using
inexpensive twisted-pair wiring.
EIA-422 (RS-422) drivers are designed for party-line applications
where one driver is connected to, and transmits on, a bus with up to ten
receivers. EIA-422 (RS-422) allows long distance point-to-point
communication and the drivers are designed for true multi-point
applications with up to 32 drivers and 32 receivers on a single bus.
The default values for EIA-422/485 (RS-422/485) communication are
19200 baud rate, 8 data bits, 1 stop bit, and no parity. The maximum
rate is 57.6 Kbps.
EIA-422/485 (RS-422/485) communication modules include LED
indicators that display the status of receive and transmit activity. Refer
to
Tables 5-8
and
5-9
.
Table 5-8. EIA-422 (RS-422) Signal Routing – Comm3, Comm4, and Comm5
Signal
RS-422
Function
Terminal
A
RX +
Lit when module (Comm3, Comm4, or Comm5) is currently receiving.
1
B
RX –
None.
2
Y
TX +
Lit when module (Comm3, Comm4, or Comm5) is currently transmitting.
3
Z
TX –
None.
4
COM
Common Ground.
5
Table 5-9. EIA-485 (RS-485) Signal Routing – Comm3, Comm4, and Comm5
Signal
RS-485
Function
Terminal
A
RX / TX + Lit when module (Comm3, Comm4, or Comm5) is currently receiving.
1
B
RX / TX – None.
2
Y
No Connect Lit when module (Comm3, Comm4, or Comm5) is currently transmitting.
3
Z
No Connect None.
4
COM
Common Ground.
5
Caution
You can induce ground loops by tying commons from various modules
together.
EIA-422/485 (RS-422/485) communication provides EIA-422/485 (RS-
422/485) signals on the Comm3, Comm4, or Comm5 port, depending
on where you have installed the module. Wiring should be twisted-pair
cable, one pair for transmitting, and one pair for receiving. The EIA-422
(RS-422) module uses four wires and the EIA-485 (RS-485) uses two
wires for connectivity.
5.8.1 EIA-422/485 (RS-422/485) Jumpers & Termination Resistors
Four jumpers—J3, J4, J5, and J6—are located on the EIA-422/485 (RS-
422/485) communication module (see
Figure 5-5
). These jumpers
determine the mode in which the module runs (RS-422 or RS-485) and
if the module is terminated.