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Modbus RTU, with baud rate 2400, does not function correctly


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I wrote a test program to test our Modus Slave units. The Unitronics UPS-104-B10 is a master talking to 6 of our slaves. I've written test programs on the Unitronics for the following BAUDRATES 2400, 4800, 9600, 19200, 38400, 57600. 

All the Baudrates function correctly except 2400.

I've even slowed down the trigger timer to allow a 2-second delay between Aperiodic Triggers.

My SLave device reacts to all messages and replies correctly, The T3.5 spacing and T1,5 spacing are also correct (monitored on sniffer)

I also verified the messages on the UART side (Before RS485).

The CRC values are correct.


The problem is that when the PLC does a Read Holding, the value returned from the slave does not reflect in the TAG in the PLC. It stays zero.


Is there a trick to use 2400 BAUD?



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  • NoamM changed the title to Modbus RTU, with baud rate 2400, does not function correctly

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