| How complex is your application ? Digital's BASEstar package(s) would
be one approach if this is a big factory automation project. See VTX IR
for details. For smaller projects it could be overkill, in which
case...
A long time ago, Modicon used to do an OS-independent package (shipped
as source) called Modcom. You provide a serial line and implement a
routine to send data down it (difficult, huh?) and compile the rest of
the routines provided as source and then call them from your own
program.
I have no idea whether Modicon still sell Modcom.
If they don't, the Modbus protocol isn't too difficult to build your
own. (I've some Fortran you could start with if you were desperate).
The one thing to watch for with RTU mode is that you need a transparent
non-packetising link between host and PLC. You can't use a terminal
server or other device which packetises data. In RTU mode, the protocol
uses an inter-character timer to signify end of message, packetising
the data truncates the messages and it all goes horribly wrong.
regards
john
|