MadModder

I wasn't sure what you meant but I did switch two of the pins inside the plug around after the first issues. I... didn't consider to check the other leads but it turns out the way it was with the middle two wires flipped was correct. I'm not sure what the first problem was. Maybe something stupid like I had the connector set over a pin.

Everything seems to work now but the Z axis. Sharing the one controller it doesn't have the torque to lift the Z axis. Is there any way to configure marlin to make use of that spare 2nd extruder controller?

Edit: Forget that last one, just found the right combo of things to google search. Also thanks for the help Andrew.

You and me both Tom 

I've just spent the evening gleaning all the 'I bits' (ie inputs) from the circuit diagrams  that I have and typing them into a cross reference file that STEP5  uses to translate absolute labels (such as I 8.1) into symbols.

Next task is to do the same for all the outputs (Q bits) from the  circuit diagrams, then try and pick up the internal 'standard' flag words from the 'Guide to writing PLC programs from Siemens.

Hopefully when those tasks are completed the 33 pages of program will be more user friendly bed time reading 

. . . of course all this effort is no guarantee that the 'M20' issue that I'm seeking will be revealed, or indeed that the issue is even IN the PLC 

Continuity seems okay. I switched out the stepper driver and that didn't do anything. My best guess is that either the stepper motor itself is damaged or the approximately 3 meter long cable is too much for it. I'll try exchanging the motor for the extruder motor I suppose.

Edit: Motor is fine, tried hooking the Y motor to the X output and that runs fine. The problem must be with the cable. I guess I could try measuring resistances but I hope the issue isn't just the length.

Using a stepper motor instead of a plain dc motor would allow you to move the head a specific distance.

So continuing on the theme of self education, and boring the pants off you, segment 1 translates as follows:

Segment 1
:STL
:L KH 0202        Load Hexadecimal 0202 into Accumulator 1-L
:T FW 121           Transfer contents of Accumulator 1-L into Flag Word 121 bits 8-15 to byte n, bits 0-7 to byte n+1
:L KH 0020        Load Hexadecimal 0020 into Accumulator 1-L
:T FW 119           Transfer contents of Accumulator 1-L into Flag Word 119 bits 8-15 to byte n, bits 0-7 to byte n+1
:***

Which can only be represented as a statement list, as flowchart or ladder are not appropriate