Dz! Posted February 24, 2020 Report Share Posted February 24, 2020 (edited) I try to exchange some data between Unistreams using MODBUS. Communication is one-way, only reads, no writes. I have 12 periodic INT32 reads (at rate of 500ms) set up + 124 periodic single bit reads (at rate of 250ms). At bit 114 it fails with status 2. All other bit reads finish with status 0. Suggested queue length reads 16. No extension. I'm reading 2 slaves of the same type an software version, and both perform exactly the same. I tried with 3rd party MODBUS scanner software, and there is no problem reading the address. EDIT: I found the answer as well. The very final bit (bit 123) was not defined on the slave. Thus it was simple 'read past end of data', and by saying status 2, at some place not far from the end, it simply informs that last byte of packed bit data could not be correctly read. That's a good lesson learnt working with bit data on MODBUS. However the question still stands - is there any practical limit (in terms of available processing time), how many bytes could be exchanged using MODBUS TCP? Edited February 24, 2020 by Dz! Found solution Quote Link to comment Share on other sites More sharing options...
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