There's another little point to be aware of - in the manual it says, if you aren't using the Encoder inputs for an Encoder (you can use them as further digital inputs, in that case) you
CAN delete the Encoder entry in the Declaration part of the FB. If you aren't using the Encoder inputs
DO delete it - otherwise you'll get spurious consistency faults which you can't pin down - that one
was courtesy of the Siemens Hot-Line!
OK, now for the next one that cost me another couple of days - once again, the Hot-Line couldn't help, although I suspect if they'd hit upon the idea of asking me to e-mail them my project, they would probably have found it fast enough. Unfortunately they didn't, they just wasted about half-an-hour on the telephone.
This concerns the parameterisation of the FBs for Normal, or Debug operation and in particular the parameters for the CPU_In and CPU_Out DBs (for those just reading out of casual interest, these DBs are used to channel the communication between the CPU and the FM352-5). As you can see, the inputs are entered as DB5.DBB0 and DB6.DBB0. The fact that you
MUST use this format and not just DB5/6 or DB5.DBX0, etc., is not emphasised anywhere, but, as they say, it is in the manual!
Those were the worst problems, the next question - was it worth it. To that the answer is a resounding
YESSS !
On my little test programs I'm generating delay times of 10µS up to 2 Secs, I'm getting synchronisation better than 2 µs - ON A PLC!!! Admittedly this is a very simple small program which fits entirely into the 12 phases of the 1 µs cycle. The real program, which is much larger will undoubtedly spill over several cycles, but I'm still hopeful that it won't deteriorate much. I'm certainly convinced that not only am I going to beat the 100 µs accuracy that I talked the customer into, with a little bit of luck I'm going to beat the 10 µs accuracy he actually wants. The Trigger delays were originally planned to be handled by a specially built "Black Box", which would undoubtedly have cost a large multiple of the 850 € that the FM costs.
So if you need really high speed response in your next project, don't forget this baby - by the way, that goes for you non-Siemens people as well, the FM352-5 can also operate completely autonamously, so you can easily integrate into another system to deal with the high speed part of the job.