Rockwell-automation 1766-Lxxxx MicroLogix 1400 Programmable Controller User Manual download pdf (Page 326)

286 Rockwell Automation Publication 1766-UM001H-EN-P - May 2014

Appendix F MicroLogix 1400 Distributed Network Protocol (DNP3)

and all events of class 1, 2 and 3 are reported. Since Hold Times are configured to

5 seconds, generated events will be reported after 5 seconds.

Collision Avoidance

The MicroLogix 1400 controller currently supports the first of the two methods

listed below for collision avoidance.

• Detecting transmitted data (TX/RX line on RS485 communication).

• Detecting out-of-band carrier (DCD on RS232C communication).

When the MicroLogix 1400 is connected to RS485 network, it monitors all data

on the link. If the MicroLogix 1400 is preparing to transmit a packet and finds

the link busy, it waits for an interval defined by the Backoff_Time until it is no

longer busy.

Backoff_Time = Pre Transmit Delay (x1 ms) + Max Random Delay (x1 ms)

The Pre Transmit Delay (x1 ms) in the Link Layer Channel Configuration file is

a fixed delay and the Max Random Delay (x1 ms) in the Channel Configuration

file is a maximum random delay for Channel 0 and Channel 2. You must specify

those parameters to get the collision avoidance mechanism.

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