--- In Don Mathis <> wrote:
>
> Got it, Will let you know when complete.
>
> Don Mathis
>
>
> wrote:
>
> >>The modbus messages sent by the TS-7200 are correctly received by the
> >>S7, but the answers sent back from the S7 to the TS-7200 device have
> >>the most significant bit of their bytes set to zero, regardless of
> >>their real value.
> >>
Hi Don:
I am also working with S7-200 and modbus... I wonder if you could
confirm something for me.
At least in my case, the S7-225XP we're working with doesn't appear to
set the exception code properly; it is always 0. The returning packet
has the error bit set, but the exception code byte is 0.
I don't know if this is a bug in the S7-200 modbus library or a bug in
my library.
You can test this easily enough by sending a modbus write (0x10) to a
bogus address; the PLC should return a modbus packet like this:
[Slave Address] 0x90 0x02 [checksum]
I've been all through my modbus code and I can't find an error, but
that doesn't mean there isn't one....
Thanks,
--Yan
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