Rockwell Automation 1785 PLC-5 Manuel d'utilisateur télécharger pdf (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.

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Rockwell Automation 1785 PLC-5 Manuel d'utilisateur Page 155