SeM Posted September 27, 2012 Report Share Posted September 27, 2012 Hello everyone, I have two devices on the same RS485 line: one is a standart MODBUS RTU device, the second uses its own protocol in ASCII code. COM2 is configured to 9600 n 8 1 and I use positive pulses with 1 sec timing to activate Protocol Configuration FB and MODBUS Configuraton FB. The cycle starts with the ASCII device, then after getting the reponse I switch to MODBUS and get the required data, but when I switch back to the first ASCII device, even though OPLC sends the data, I receive no response. If I try to send the same data again, I get the response and proceed to MODBUS request and so on and so on, but the fist ASCII request after MODBUS gets no response, while the second request straightaway gets the data. Both the device work perfectly well independently, and I have tested the above described cycle both automatically and manually, so I am pretty sure it is not a timing issue. Would anyone kindly advise me on the situation? Is it an OPLC issue (something to do with buffer clearing in Modbus mode) or maybe it is a Modbus slave issue (ie commnication ports dont close or else)? Unfortunately I am not that good with Modbus yet, and googling the problem didnt help. Quote Link to comment Share on other sites More sharing options...
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