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Unread October 17th, 2019, 05:00 PM   #4
GSNITZ
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Join Date: Jun 2017
Location: TULSA
Posts: 30
To close the loop on this, we discovered another device on the network was not adhering to the Modbus standard for a minimum time between frames requirement (also known as silent duration). We were able to log the network and determine that the delay between when the master requested data and this other slave responded was very short (between 1-5ms typically). The M258 was configured for the minimum acceptable interframe delay for the given baud rate (3ms). Any frames which were received before the silent duration timer expired were flagged as RX Message Errors. After a certain number of these errors were logged, the MBS port would stop responding. We were not able to determine why exactly the port would "lock-up" and stop responding; it may have been related to a hardware level bug in the serial port, however this is pure speculation. We resolved the issue by installing a gateway between the serial network and the M258; the gateway still flagged these fast messages as RX Errors, however the gateway itself has never stopped responding. The equipment has been operating with the fix in place for several months at this point in time without any further losses of communications.

Last edited by GSNITZ; October 17th, 2019 at 05:02 PM.
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