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ET200s - Modbus Communication on RS485

8/3/2012 8:53 PM	Rate (0)
guillaume.braillon Posts: 11 Rating: (0)	Hello ! My question is about the Modbus communication on RS485 connection. I have already done a program able to interface a computer with a IM151-8 PN/DP ST CPU of ET200s PLC using a RS232 serial interface by means of the module whose PN is 6ES7 138-4DF11-0AB0. I configure the PLC as master and the computer is the slave. Now I am trying to use the same module to exchange holding registers by means of a RS485 Half-duplex serial interface. I can check the "send" request is done thanks to the Modbus simulator running in the computer or the SEND_IDB (S_SEND_SI_DONE = TRUE) and data are sent from the computer to the PLC. However, I cannot read the registers because there is an error (S_RECV_SI_ERROR = TRUE). The data S_RECV_SI_WORK_CNT_ERROR increments everytime. I guess it is not a wiring mistake because the "send" request is fine. Can you please help me to find the problem ? Thank you Best regards Attachment MODBUS_DB.jpg (468 Downloads)
guillaume.braillon Posts: 11 Rating: (0)
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8/4/2012 11:35 AM	Rate (0)
jklm Posts: 1742 Rating: (309)	Hello, I see an error code 0830 in the DB. In this manual: http://support.automation.siemens.com/WW/view/en/9260793, page 211, the error code is explained Extract: Master: A request message frame has been sent and the response monitoring time has elapsed without the start of a response message frame being detected. In other words, you did not get a response. Remedy from the manual: Check whether the transmission line has been interrupted (interface analysis may be necessary). Check that the same settings have been made on the module and communication partner for the following protocol parameters: transmission rate, number of data bits, parity and number of stop bits. Check that the value for the response monitoring time in PtP_PARAM is large enough. Check whether the specified slave address exists. The Modbus master system is only allowed to use the broadcast function for the function codes enabled for this purpose.
jklm Posts: 1742 Rating: (309)
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5/26/2015 10:07 AM	Rate (0)
Min_Moderator Posts: 4757 Rating: (122)	New question published by s23 is split to a separate thread with the subject G120, rotate the motor speed with different RPM's. Best regards Min_Moderator
Min_Moderator Posts: 4757 Rating: (122)
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