Postby MKB » 26 Apr 2011, 11:27
If the YJM footswitch is like many of the other stompware footswitches in the Marshall line (using a standard guitar cable between the footswitch and amp), it is basically microcontroller based, and it talks to a microcontroller in the YJM itself. I seriously doubt if Marshall would give out any code details for the footswitch or YJM. If you are very clever, you could try looking at the switching signals with a logic analyzer, and reverse engineer it that way, but that would be difficult and there is an easier way to skin that cat.
You could possibly enable external midi switching by gutting a YJM footswitch and using its PCB as an interface between the midi switching system and the YJM. The midi switcher would need momentary switch outputs to activate the individual switches on the YJM footswitch, plus you would need to add jacks or a connector to access the individual switch terminals in the YJM footswitch. This would be the easiest and cheapest way to do it I'd think.
I just can't help having the nagging feeling that, buried inside the YJM, there is an unused microcontroller pin with a midi compatible UART on it. I haven't seen a schematic or code (would dearly love to though), but if I was writing the code, I'd have one in there if a pin was free. It's just too easy to set everything at 31.25Kbaud. Time for another cup of coffee, my mind is drifting.....