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I've found 200 lines of code which do a simple example, and I'm going to give that a go. Our need is pretty basic, so having code we have hacked ourselves is probably reasonable.

I need to implement a simple-minded modbus-TCP slave in an embedded Linux system. My first port of call would have been TuxPLC, but that seems to have evaporated - anyone know why? In the absence, does anyone have a recommendation about where to start? There seem to be a couple of commercial...

Thanks OldPfart I'm just going to hope that we never come across anything in BCD. What Omron models feature this 64-bit fpt then?

Thanks - I've got a flowmeter in front of me that uses 32-bit fpt, and heaven help me, ASCII strings in modbus registers. I don't THINK it uses signed integers, but I haven't looked at all 100 registers yet :-( David

Thanks mls1, We've got our own s/w in a box see http://www.dexdyne.com/netrix which does the Modbus reads. It will use a block-read on any adjacent blocks of registers, so we're half way there. The Modbus driver at our end is home-brewed, and I'm going to have to get the programmer guy to...

I am aware that Modbus is seen as a set of 16-bit registers. I am aware that some of the numbers I'll want to read across a Modbus will need >1 adjacent 16-bit registers - floating point for instance needs 2 or 4. Similarly some data will neeed 32-bit integers, which could suffer in the same...

Thanks Skogsgurra, I meant to say IEEE 754 - I can never remember either. Are you saying that I might encounter all of them, except the non-2-s-complement signed stuff? Do some PLCs really have 64-bit fpt? I know it's what PCs default to these days, so I guess PLCs will not be far behind...

I'd like to find out what number formats are in use in a representative range of PLCs. I guess there's nowhere better to ask ??? We're reading values out of them across modbus. I want to know what possible formats I an expect to meet. I don't know how much flexibility the PLCs give to the...