Rockwell Automation 1785-Lxxx Enhanced and Ethernet PLC-5 Programmable Controllers - Manual (Page 155)

Publication 1785-UM012D-EN-P - July 2005
Communicating with Devices on a Serial Link 10-5
Polling Inactive Priority Stations
Through the channel configuration feature of your programming software,
you can choose to poll one or all of the inactive priority stations when the
PLC-5 controller is in master mode on channel 0. The default selection is to
poll one inactive priority station during each polling sequence.
If you choose to poll all inactive stations, you are alerted immediately when an
inactive station becomes active; you do not have to wait for all of the other
polling sequences to complete. Polling all inactive stations might slow down
channel performance.
Changing Modes
Configure channel 0 of the controller to change communication modes via:
• the channel configuration screen in your programming software (in
program mode only) ; or
• communication mode change characters (ASCII control characters) sent
remotely to the controller, which switches modes
Cabling The following table lists the maximum cable lengths you can use with
channel 0.
Port Transmission
Rate(s) Maximum Cable
Length
RS-232C All 15 m (50 ft)
RS-422A
(compatible) All 61 m (200 ft)
RS-423 All 61 m (200 ft)
IMPORTANT
Follow these guidelines:
•
When channel 0 is configured for RS-422A compatibility, do not
use terminating resistors anywhere on the link.
•
When channel 0 is configured for RS-422A (compatible) and
RS-423, do not go beyond 61 m (200 ft). This distance restriction
is independent from the transmission rate.