anton_ztalker Posted March 18, 2013 Report Share Posted March 18, 2013 In my project on the V120-22 I use 2 COM ports for RS485 Modbus communication. Port 2 - Master mode to communicate with another device, the Port 1 - Slave mode for communication with the upper level. After some time, the PLC stops responding via Port 1, while Port 2 is operating normally and ladder is operating normally too. Helps only restart the PLC. If Port 2 is disabled, then the connection through Port 1 is without failing. It seems, as if at the time of simultaneous access to the ports, there is a conflict. Why lost communication with Port 1? Ports settings: Port 2: 115200, 8, none, 2 Port 1: 57600, 8, none, 1 The request to Port 1 is sent after a pause of 10 ms after the last response Connection breaks after 2000-15000 requests Best regards, Anton Link to comment Share on other sites More sharing options...
MVP 2023 Joe Tauser Posted March 18, 2013 MVP 2023 Report Share Posted March 18, 2013 Upload your program. Joe T. Link to comment Share on other sites More sharing options...
anton_ztalker Posted March 19, 2013 Author Report Share Posted March 19, 2013 Upload your program. Joe T. Thanks for your response. Sorry, I can't upload the program, because I'm not the author. And the program is awkward, this can be a cause of the error. I solved the problem as follows: set the check bit SB135 (COM Port 1, Data Receive) before sending the requests to Port 2 and reduced the baud rate to 9600. Link to comment Share on other sites More sharing options...
MVP 2023 Joe Tauser Posted March 20, 2013 MVP 2023 Report Share Posted March 20, 2013 Glad to hear you got it working. I've often found high baud rates to be problematic on RS485 when communicating between devices. I usually use 19.2 or 9600. joe T. Link to comment Share on other sites More sharing options...
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