AB to Modbus transfer question.

[semilogical 0]

When transferring information from an integer file in a SLC-1100 (or any SLC with modbus capability) is there any impact on the value in the modbus word? I'll give an example of what I'm sending: I will be sending N7:0 to a modbus location through a CEV module. I'm currently unsure of the offset that will be used but if N7:0 goes to modbus address 401001 and N7:0/0 is 1 will the same bit be a 1 in 401001? (401001.1) I understand the LSB in AB land is 0 but in Modbus land it is 16. Will my transferred value reside in 401001.1 or in 401001.16?

[b_carlton 61]

I have used MODBUS from the Micrologix units to two types of drives, a Powwerflex 4 and a Control Techniques. In both cases there was no problem with bit order.

[paulengr 44]

It's a Micrologix 1100, not a SLC-1100. For all intents and purposes, the SLC line is "dead". Micrologix PLC's use the same compiler/programming environment but that's where the similarities end. The Modbus MSG instruction in a Micrologix automatically does big/little endian conversion at least when it comes to 16 bit words. I believe there is an issue with talking with modbus "coil" (bit) registers but since I've rarely used anything except the 3.... and 4.... series registers, I'm unaware of what those issues may be. If you can do so, I suggest you start with reads on known data values first. That way you can work your way through any issues that may arise because of differences in terminology with regards to bits and words.