[Visual-devel] Re: Modbus module (was: Re: [MAT-devel] Re: Re: Re: MATplc - VISUAL interface)

[Thomas H. <Tho...@we...>]

Hello Mario,
> Thomas Hergenhahn wrote:
> > ...connection. Keeping the connection would be better with VISUAL.I tr=
ied to set
> > it to false, but the modbus module opens a new connection for each tra=
nsfer.
> >=20
>=20
>=20
>  Strange! I'll have to check on why it is doing that!
>  Either we have a bug in our modbus module, or else it is not receiving
> the response packet from the slave, and assumes that the connection has
> an error. In that case, the modbus spec. says we should close the
> connection and start up another!
Oops, this may be my fault. I must check whether I give a correct answer.
>=20
>=20
> (...)
> >=20
> > 2. 32 bit and floating point:
> >  I tried to get values from the oven demo. I inserted into the maPLC.c=
onf:
> > map out digital=5FIO.out=5Fword.1 TFTemp
> > In principle I get some number, but in a 2 bytes (word) message. Is th=
ere a
> > way in modbus protocol.
> > a) to transmit a 32 bit value=3F
>=20
>  It should be transmitting all 32 bits of the float. Yet another issue I=

> will have to check out.
There is a notice in the source about currently supporting only 1 word tra=
nsfers with function=20
code 16.
I wrote some extensions and can transfer float now (without type informati=
on)
>=20
> > b) to transmit the type float=3F
>=20
>  I don't think so. Modbus has no concept of variable types. What we
> should/are doing is casting the 32 bit float onto a unsigned 32 bit
> integer, and sending that integer instead!
Ok, this is what I do at the moment, sending the 4 bytes which make up a f=
loat as two words.=20
Only that the manual confuses me about endianess and which byte should go =
where.
Wish I had a real world modbus conform device to test what IT does.
>=20
>  Yep, this is intentional. It seems that this is the modbus way of doing=

> things. It got me confused too at the beginning. Somebody convinced me
> that this is how it should be. If you can convince me otherwise, it is
> trivial to change it once again!

Ok, I RTFSpecification and found it is said to be this way.

Cheers,
Thomas


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