pbosscha
Has any one seen the following:
Using MODBUS/RTU to talk to some devices and then using RADZIO! to check results against OpenPLC. For some reason OpenPLC does not pass on the Input Status (%IX100.0 - ) at all.

Wrote a program to interpret %IX100.0 thru %IX100.7 and stuff that into a Holding Register, and that works fine.
This tells me that OpenPLC gets the status correctly, but this is not passed to the MODBUS TCP side.
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pbosscha
Whoops, sorry, found the problem ... caught out by addressing. On Radzio one has to look at address 800, not 100
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thiagoralves
A lot of people are having issues with OpenPLC addressing vs Modbus addressing. I wonder if this is a real issue. Perhaps I should just drop this byte grouping in OpenPLC addressing and make it all linear, so that it matches Modbus addressing. What do y’all think?
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rodrigo_rolle
A lot of people are having issues with OpenPLC addressing vs Modbus addressing.

Yeah, it was easy to debug on v2 because everything used to start at 0.0. Finding 100.X addresses is a little bit confusing for beginners. If matching Modbus addressing is not a simple thing to do, you could at least add some extra info to http://www.openplcproject.com/scada so that people can find the address space for slave devices more easily.
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rodrigo_rolle
Hello again! Are there Modbus addresses for discrete memory coils (%MX0.0, %MX0.1 and so on)? On the Modbus reference mapping I couldn't find this type of variable.
Thank you!
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thiagoralves
There aren’t, and I should have created those... however, you can still use any unmapped IO (something like %QX80.0 or do) as memory.
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