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M91 RS 485 MODBUS comunication

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I am using a RS 485 MODBUS communication to controll the speed of the frequency converter (Commander SK from EMERSON). I did suceed to establish the communication between the PLC and the frquency converter, but afterwards I was not able to downlaod a new PLC program to the controller. Any communication between the programing PC and the PLC was no more possible.


Can somebody give me some advise what to do? I was thinking about hardware reset or something like this.


PLC type  M91-2-R2C


best regards,



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Default communication settings for U90Ladder are 9600, 7, N, 1. MODBUS require 9600, 8, N, 1.

Check if Break is disabled or not. Break signal reset communication settings to default to allow U90Ladder communication.

You can change communication settings to 9600, 8, N, 1 and check again.

Or enter Info mode and change to "SYSTEM->STOP ?" and stop program. This allow to restore communication.

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