Knowledge Base / Protocols / Modbus

What are the causes of a -11 error code using a ProSoft Modbus product?

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A -11 is a timeout error.  The MCM master port is sending the command but it does not get a valid response from the slave back in time.   

If the port x Response Timeout setting is 1000ms, the port x LED will blink once every 1000ms.  This indicates the command is being sent out of the port.


 Common causes of a -11 timeout error:

- baud rate, parity, etc mismatch. 

- incorrect jumper setting at bottom of module (RS232, 422, 485 setting).  

- Reversed polarity

- Wiring issues, try  + and - pins only, no ground/shield.

- slave is busy and ignores the master command

- noise on the line, the message is compromised by the time it gets to the destination.


Connecting with ProSoft Configuration builder and using the Data Analyzer option in the diagnostic menu will show the Modbus traffic coming in and out of the port.  It will help determine if a response from the slave is received or if there is noise on the line.  The User Manual shows how to connect use ProSoft Coniguration Builder for diagnostics.