SysEx

Based on previous Kurzweil models, trial-and-error, old manuals, and posts on the "Mastering VAST" forum:

Sending F0 7E 7F 06 01 F7 asks the PC4 to identify itself, and it responds with

F0 7E 7F 06 02 07 46 00 01 00 34 2E 33 32 F7:

F0: sysex start 7E 7F 06 02: identifies this as a reply to the version request 07: Kurzweil 46 00: identifies the keyboard "family", I think 01 00: model 34 2E 33 32 F7: This is just ascii-encoded "4.32", the OS version. F7: sysex end

PC4: SysEx messages seem to all start with F7 07 46 01 00: 07 46 01 identifies Kurzweil and PC4's family and model, and the 00 is the default SysEx ID (which you can change with Global->MIDI->SysEx ID if you have multiple PC4's and want to address your PC4 to one of them).

This is a variation on the format described in, for example, the K2600 reference guide.

The next byte is a command; variable data may follow after that; some commands:

F7 07 46 01 00 30 F7: chooses program mode F0 07 46 01 00 31 F7: chooses multi mode F0 07 46 01 00 11 XX YY F7: selects multi XX*128 + YY

Other PC models have had a "button mode" which causes the keyboard to send SysEx messages for various buttons on the front panel. There doesn't appear to be any evidence that the PC4 can send or recieve any of those button mode messages.

Kurzweil makes an editor, so one approach might be to run the editor and watch the MIDI traffic.