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I have spent numerous hours getting Unity Pro's Send_Req function (on a Premium platform) to read Modbus 3x registers from a field device.
In short, the output from a Send_Req read of Modbus 3x registers contains 5 status bytes before the data. After processing these status bytes, the data then needs to be shifted by 1 byte so that the two bytes for each 3x register read are placed in a single 16 bit register rather than split across 2 registers. The bytes in each register then need to be swapped. (Think I am kidding with all this? - Have a try.)
It appears that the Unity Pro programmers intended to provide a single "whizz bang, do it all" function as a solution to a number of communications protocols. However, it would be nice to see them have another look at it (Preferably writing a dedicated Modbus block to handle all modbus read and write functionality.
Would be interested to hear of any other problems experienced using the Send_Req function with other protocols.
In short, the output from a Send_Req read of Modbus 3x registers contains 5 status bytes before the data. After processing these status bytes, the data then needs to be shifted by 1 byte so that the two bytes for each 3x register read are placed in a single 16 bit register rather than split across 2 registers. The bytes in each register then need to be swapped. (Think I am kidding with all this? - Have a try.)
It appears that the Unity Pro programmers intended to provide a single "whizz bang, do it all" function as a solution to a number of communications protocols. However, it would be nice to see them have another look at it (Preferably writing a dedicated Modbus block to handle all modbus read and write functionality.
Would be interested to hear of any other problems experienced using the Send_Req function with other protocols.
