elektrik85 Posted January 14, 2015 Report Share Posted January 14, 2015 Hello everyone, This is my first time ever messing around with a unitronics plc. I have a V130 I started playing with. I'm trying to learn modbus rtu, so I purchased a Solo 4824 temp controller from automation direct in order to practice. I followed the examples in the modbus help files. I want to display the controllers temperature on the HMI display. I have port 1 configured as RS485. The cable goes to a terminal block and from there I use pins (+)1 and (-)6 to go to the temp controllers data A and data B terminals. I've tried for a week to connect to the Solo controller but no luck. I used the loopback test function block but get no response. I configured modbus and a read holding register function block in the plc logic but have not gotten anything. I am reading all I can on modbus rtu since this is my first time ever using it and want to eventually implement it at work for some other units that use modbus rtu. Please help. Any information would be appreciated. Quote Link to comment Share on other sites More sharing options...
Eyal Koren Posted January 14, 2015 Report Share Posted January 14, 2015 Hi elektrik85, Did you change the jumpers inside the V130 to RS485 mode? You can read more in the V130 installation guides, found here Quote Link to comment Share on other sites More sharing options...
elektrik85 Posted January 14, 2015 Author Report Share Posted January 14, 2015 Hi Eyal, Yeah I changed the jumpers to rs485 and also left the termination on. I am not really sure what the termination is used for. Should I have a termination at the temp controller also? Quote Link to comment Share on other sites More sharing options...
MVP 2023 Joe Tauser Posted January 15, 2015 MVP 2023 Report Share Posted January 15, 2015 Post your code so we can see if you have the serial port configured correctly. I have actually written a program to access the Solo control and it works; the hardest thing in serial communications is making first contact. I feel your pain. Joe T. Quote Link to comment Share on other sites More sharing options...
elektrik85 Posted January 17, 2015 Author Report Share Posted January 17, 2015 Hey Joe, Here is the code I have written. Thank you. Test.vlp Quote Link to comment Share on other sites More sharing options...
sunit Posted January 17, 2015 Report Share Posted January 17, 2015 Also check the parameters of the temperature controller like slave ID, Baud rate , Stop bit , parity and modbus address Quote Link to comment Share on other sites More sharing options...
Eyal Koren Posted January 18, 2015 Report Share Posted January 18, 2015 Hi Eyal, Yeah I changed the jumpers to rs485 and also left the termination on. I am not really sure what the termination is used for. Should I have a termination at the temp controller also? The terminations is crucial for the correct function of an RS485 network. In such network, the two end nodes must have either the termination jumper set to on, or alternatively a resistor (typically 120 Ohm) between the + and - signal line. The termination has two main purposes - to prevent data corruption and to minimize electric noise. For more information please see the attached guide for RS485 (taken from Visilogic help). RS485.pdf 1 Quote Link to comment Share on other sites More sharing options...
elektrik85 Posted February 1, 2015 Author Report Share Posted February 1, 2015 Post your code so we can see if you have the serial port configured correctly. I have actually written a program to access the Solo control and it works; the hardest thing in serial communications is making first contact. I feel your pain. Joe T. Hello Joe, Was the code I wrote correct or am I missing something else? I also went ahead and put a 120 ohm resistor on the temp controller but I still get no where. Thank you. Quote Link to comment Share on other sites More sharing options...
Eyal Koren Posted February 3, 2015 Report Share Posted February 3, 2015 Hey Joe, Here is the code I have written. Thank you. You set a bit to send the modbus command but didn't reset it after the command had been executed (see image). 1 Quote Link to comment Share on other sites More sharing options...
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