Questions about Modbus data model with only 1 block


Thread Starter


A vendor implemented a Modbus data model with only 1 block (see model B). I think, it is not full modbus compliant. Perhaps someone can help me.

Here yo can see, how I understand a Modbus data model with only 1 block:

And here the vendor implementation:

Here are an example with Modbus Poll and the vendor implementation:

Lynn August Linse

This product is fine, in fact it looks rather good! It is extremely common for coils (the 1-bit read-write) to be 'mirrored' also as 16-bit words. Probably 90% or more of the products on the market do this.

Yes, this means writing a bit will cause a register to change 'magically', but data within a control device changes by itself all the time.

NOTHING in Modbus forces any particular hardware design. You read or write bits or 16-bit words; how these map to data or the real world is merely a matter of paper or PDF documentation.
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