Rockwell Automation Publication 2080-UM002M-EN-E - April 2022 123
Chapter 6 Micro870 Controller Distributed Network Protocol
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.
After the Backoff_Time, the controller tries again, either indefinitely, or up to a
configurable maximum number of retries. If a maximum is used, the protocol
considers this as a link failure.
Time Synchronization The time value in the real time clock (RTC) of the controller (firmware real time
clock) or plug-in module (2080-MEMBAK-RTC2 or 2080-SDMEMRTC-SC) is
updated every 1 second.
The DNP3 subsystem and the RTC (firmware or plug-in module) are
synchronized by the following conditions:
•power up
• a request for time synchronization from DNP3 Master.
At power up, the DNP3 subsystem gets the time from the controller. For the
controller to acquire the correct time, a plug-in module RTC should be used
and enabled before a power cycle to acquire the correct time from the
controller. The firmware RTC always reverts to a default time and date after a
power cycle, so it is not able to provide an accurate time to the DNP3
subsystem.
If a plug-in module RTC is not used, then the firmware RTC must be enabled.
To enable firmware RTC, select Enable firmware real time clock.
When there is a write request for time synchronization from a DNP3 Master,
the time in the RTC (firmware or plug-in module) is synchronized with the
time from the DNP3 Master.
This table shows the 2080-MEMBAK-RTC2 plug-in module Accuracy.
Configure the Time Synchronization Interval in the Micro870 DNP3 Slave
configuration according to this table, so that a DNP3 Master can send the time
synchronization request periodically for more accurate times in the controller.
2080-MEMBAK-RTC2 Accuracy
RTC Accuracy
(1)
(1) These numbers are maximum worst case values over a 31-day month.
Ambient Temperature
±5 sec/month 25 °C (77 °F)
±9 sec/month -20…+65 °C (-4…+149 °F)
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