Do the previously set signals return to their original state when you set more than 4 signals? If so, then your C64 already has a PLC program in it that is running. Note that the C64 has a PLC that is integral to it. If a particular signal is not being set by the PLC, then any signals you set through the PLC I/F screen will stay in the state that you set them. You may need to download the existing PLC program from the C64 (if you need to save it) and write a minimal program that you can test the drives with. Mitsubishi's offline PLC development software is called GX Developer.
Scott |