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Showing results for tags 'read_var'.
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hello, Somebody have suggest how need read data from slave using modbus RTU. I am using M241 PLC and read_var function. The picture you can see my PLC program. The data of slave is placed 3394 address. Then I try to read, always "READ_VAR" function get "CommError" which number is 254 that means "The detected operation error contains protocol- specific code" and "OpenError" which number is 3 that means I don't know. How need read from slave data, which modbuss adress is 3394?
Hi all, currently as part of a project I am trying to communicate between a Schneider M340 plc and an Allen Bradley micrologix processor. I am programming the M340 and the micrologix has been installed by another supplier. they have mapped the Modbus registers on their side and given me a spreadsheet with these. I am able to read values with no issue but I cannot write values back. i've included a screenshot or the read_var and write_var instructions I am using. I would really appreciate any help if anyone has any insight on this Mark