It seems that 1 out of 5 posts on this forum is about some form of Modbus. This is an indication to me that there is a design or documentation error with Modbus XXX,
I/we have found that supporting Modbus XXX is a time sink. There reason why is that the Modbus RTU version is timing dependent and few can implement the timing requirements especially when trying to transmit at rates over 9600 baud. How does one measure 1.5 or 3.5 character times on a PC or PLC? You can't. Another issue is that the specification doesn't cover how REALs, DINTS or DWORD are transferred. It seems that everyone does their own thing and assume it is right and everyone should do what they do.
We took a different approach. We used a Modicon/Schneider PLC as the reference. We can transfer 32 bit values back and forth with Modicon PLCs with no problem. However, not everyone is taking the same approach so often bytes or words need to be swapped around to the format they need.
When Modicon decided their PLC supported 32 bit REALS they should have updated the specifications on byte and word ordering. This was not done so Modicon TCP and RTU are still a pain and a time sink to implement.
There needs to be a new simple standard that at least can send data back and forth on 32 bit boundaries.
I/we have found that supporting Modbus XXX is a time sink. There reason why is that the Modbus RTU version is timing dependent and few can implement the timing requirements especially when trying to transmit at rates over 9600 baud. How does one measure 1.5 or 3.5 character times on a PC or PLC? You can't. Another issue is that the specification doesn't cover how REALs, DINTS or DWORD are transferred. It seems that everyone does their own thing and assume it is right and everyone should do what they do.
We took a different approach. We used a Modicon/Schneider PLC as the reference. We can transfer 32 bit values back and forth with Modicon PLCs with no problem. However, not everyone is taking the same approach so often bytes or words need to be swapped around to the format they need.
When Modicon decided their PLC supported 32 bit REALS they should have updated the specifications on byte and word ordering. This was not done so Modicon TCP and RTU are still a pain and a time sink to implement.
There needs to be a new simple standard that at least can send data back and forth on 32 bit boundaries.