Rockwell Automation Publication 2080-UM002N-EN-E - November 2022 113
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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