Profibus Master Code.

sagittarius schrieb:

"simple" and "profibus" are mutually exclusive.

Tilmann

--
http://www.autometer.de - Elektronik nach Maß.

You should really get some background information about Profibus, before you even start to dream about implementing something with it.

Start for instance with

but I would really suggest reading some tutorial book about Profibus, e.g. "The New Rapid Way to Profibus DP" by Manfred Popp, which at least some have liked.

Siemens PLCs are hard to use and you would definitively need a configuration tool to do anything useful with it, so you would anyway need a PC with a Profibus card and some configuration software.

While Profibus-DP (but not Profibus-PA) is simply RS-485 with asynchronous characters, there are some problems. Most of the speeds are not standard serial communication speeds, so at least a special crystal is needed for the baud-rate generator.

The Rx/Tx timing is critical, so the 16550 type family UARTs are practically useless, since it does not have hardware Rx/Tx RS-485 line control or even a usable "Tx shift register empty" interrupt instead of the "Tx data register empty" interrupt found on 16550.

To fully qualify for proper poll cycle timing, most PC type operating systems (such as Windows or Linux) have far too much latency, so in practice, all Profibus PCI cards use some kind of ASIC doing the actual Profibus-DP cyclic polling.

Paul

It has been a while since I used profibus and industrial controllers in general, but I remember a couple things. One was that there was no "simple" profibus.

There's more than one "flavor" or "mode" of profibus, to begin with. Most (all?) Profibus devices us an ASIC from Siemens to interface with the profibus.

If all you want to do is read and write the PLC, I think you can do it more simply through the serial bus and the Modbus protocol, if Siemens supports it. This probably isn't available in the smallest PLC'S.

You might try Siemens...

While Modbus has been recently available for some Siemens PLCs, the old Siemens 3964R/RK512 serial protocol should be available for a large range of PLCs.

Paul