We have a Proface AGP3300H hand-held hmi connected to a Panasonic FP-X plc using RS232 serial comms. via the plc tool port. With the plc in STOP mode, the screen works perfectly. With the plc in RUN mode, the screen just freezes up, doesn't display any states or values and doesn't even let us navigate from page to page.

We have triple-checked all the comms., settings, cable connections and so on and can come up with nothing obviously wrong. We have tried various Baud rates, flow control settings, retries and wait times, all to no avail. Has anyone else seen this problem between FP-series plc and Proface screens and if so is there a solution please? We have contacted Proface who don't have an immediate fix but are looking into it and we are concerned that the FP-X, being a fairly new Panasonic model, may have some idiosyncracies we aren't aware of.

Additional information from the OP:

1 - The Proface program works perfectly in simulation mode.
2 - We tried creating a very simple program with just one screen page, two pushbuttons and one numeric input field and that does exactly the same thing - so it isn't an issue with quantity of data or bad addressing.

Can you check the Panasonic FP-X program. Maybe something in run mode is locking up the port. Check for port settings in the Panasonic and the program.

Yes, because we are using the tool port (also used for plc programming) there is nothing in the ladder program connected with it. The port settings match the HMI in every respect and it does work perfectly in STOP mode. We are guessing that it may be to do with scan time and time allocated for serial comms. through the port but nothing we try seems to make any difference. Next step is to make a new plc prgram with just a couple of rungs and see if that behaves the same.