You can display the ladder on an M50, even edit it if you want. F0 key.
The ladder is the logic that controls general machine operations such as tool changer etc and all external switches and relays and communicates back and forth to the CNC side.
The function switch normally goes to 4 inputs for a total of 16 selections in binary.
If you are only getting one bit change on the screen it would indicate either the switch is not outputting the correct code or the inputs are defective.
The manuals and possibly the PLC manuals are on the MEAU website.
The one for editing the ladder is 'PLC ONBOARD INSTRUCTION MANUAL'.
The ladder display is especially usefull as it can tell you where a machine control problem is.