Niels_1980

S7-200 modbus communication with Dixell controller

3 posts in this topic

When setting up Modbus communication between an S7 - 200 and a temperature controller Dixell I knock on the following issues that are not entirely clear to me . In network 1 Set the data of the corresponding slave In network 2 to send the telegram to the slave , the answer is stored in VB384 I now want to read the temperature of the controller according to the protocol is the value in the holding register 256 , if I put value 40256 in the block MBUS -MSG I get nothing back from the slave , if i enter value 40257 i get the the temperature value of the controller . I suspect this is because the holding register start at 0 and MBUS - MSG value 40001 interprets as registry No. 0 . Is my reasoning correct in this? Second problem is that I do not get the temperature from VB384 but from VB385 ? Furthermore, the value VB385 also change (eg temperature equal to 25 ° than the value in VB385 is jumping from 25 to 5) , I now put a move instruction VB385 to VB800 whenever M0.1 comes high with a positive transition . Then, the value remains constant at the measured temperature. Does anyone have any explanation for this problem ? Included the pdf to the modbus protocol: http://www.yumpu.com/en/document/view/3871598/modbus-rtu-dixell-devices

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Hi malc cope, thanks for your reply ! I'm still struggling with another problem when writing registers to the modbus slave. In the same block MBUS_MSG i change parameter RW to 1 so that i could write to the slave to register 41281 (1280 dixell register) I have to set bit 0 from VB384 & VB385 to 1 or 0 to turn on/off the device when input 0.0 is 1, when i activate I0.0 the slave turns on for a short while and then turn off again. In the status chart VB384 and VB385 turns to 0000 0001 when the input is activated and also put the device ON, but when I0.0 is released the values going back to VB384 0000 1000 and VB385 0000 0101 When i activate I0.0 for a few seconds the values stay but the block MBUS-MSG M0.1 isn't showing the state ready, it looks like the system hangs itself. When i reboot the plc (stop / run) it will work again. Thanks in advance,

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