modbus rtu

[alikaptan]

hi can you share a short data sending and sending program with modbus rtu? The current library is a little difficult to make a complex meaning, can you share a short code to understand?

[temtronic]

quick answer...
MODBUS IS complex !!! There's no such thing as a 'simple' program...
one reason why I don't use it.

Jay

[dluu13]

Did you only check out the library files, or did you also check out the modbus master and slave examples in the example folder?

Even then, it only shows you one example of how you might implement modbus in your system. There, they have a couple of arrays for your various registers. Modbus is a protocol. Where you choose to point your hold/input registers and stuff is totally up to you.

Nevertheless, the examples work pretty much out of the box. If you just want to use Modbus, without needing to understand all the nitty gritty details, that'll work fine.

[Gabriel]

I'll bite.

Temtronic, this is your second (this week at least) post with a bad rep for modbus.

What is the +30 year old hacker proof 24 baud protocol?
I am genuinely interested. I find a lot of "old" tech is better tech, which can be rebooted with new hardware to make it even better.

So, what is it?
_________________
CCS PCM 5.078 & CCS PCH 5.093

[Ttelmah]

His communications may well be proprietary.

I use ModBus quite a bit, and share the hatred of it....

It was originally designed for a particular family of PLC controllers. It's
supported data types, and operations were all designed for these controllers,
rather than for more general use. The only reason it became popular, was
that it was quite well documented, and usable 'royalty free'. Unfortunately
this has led to widespread adoption, at a significant 'cost' in terms of
actual convenience...

For most applications that do not require the ability to connect to other
devices supporting ModBus, you are much better off designing a protocol
that actually does what you want.

Now (for example), you can take advantage of the ability to use 9 bit,
and have the 9th bit as a 'command' flag. Then if you allow (say) 32
devices to be addressed, and use a byte for the address, you still have
three bits left in the address range. So (again for example), use these
as a range of indicators, with '000' meaning 'command is for this device
only', perhaps '001', as 'command for all heating units', etc. etc..
Allows you to massively reduce the number of transmissions needed.
Similarly, if RS485 is the hardware, then implementing multi master
would allow devices to send alerts without having to be polled. Or you
could have an extra 'service needed' wire, and use an open collector
drive on this, have the 'slave' units pull this low when they need to
talk. Then the master doesn't have to 'poll' the slaves, until this signal
is seen to go low. With a bit of thought, the protocol becomes much
better suited to what you actually need to do. Then if the protocol is
designed to reduce the actual amount of transmissions needed, this
allows lower data rates. In terms of how far you can send and how
reliably, 'slower is better'....