With almost any piece of equipment that outputs MIDI there lurks the question of "What EXACTLY is being output by this thing, anyway?". If you're fortunate enough to be armed with a good MIDI monitor (WAZMIDI for PC DOS for example) then it's pretty easy to find out. Without such a program, however, MIDI can be a convienent nightmare. This is especially true when MIDI clock is involved. For this reason, I have put together the following information about "What EXACTLY is output from Lexicon's JamMan".
The MIDI output from JamMan is really fairly simple: when you press RESET, a "SYSTEM REAL TIME" STOP message (FC hex) is output. When you then press TAP (for the first time after RESET) a second STOP message is output (in case the slave system was manually put in PLAY). When you press TAP a second time, a "SYSTEM REAL TIME" START message (FA hex) is output. The system is always outputting MIDI CLOCK but at a default rate on power up and the last TAPed in tempo thereafter.
JamMan, by itself, does NOT output any "all notes off" messages. However, it DOES pass all MIDI data present at it's input through to it's output (soft thru) with the exception of incoming MIDI clock which is blocked. Although the MIDI spec doesn't recommend doing this, we found it really useful when driving more than one JamMan from a MIDI foot controller or sequencer.
I should point out that the tempo of the MIDI clock generated by JamMan changes IMMEDIATELY after the TAP button is pressed the second time. I've encountered problems with some sequencers due to this. CakeWalk version 3.00 for Windows would start then stop immediately after the second TAP. TwelveTone fixed the problem in maintainance release V3.01 but other sequencers may encounter the same problem. From JamMan's perspective, there is not much I can do; I don't know what the tempo is until you press the TAP button a second time. At that point you need the clock immediately.
Also note that JamMan auto-detects incoming MIDI clock and attempts to create its loop based on the tempo of that clock. This is indicated by a flickering TEMPO LED when JamMan is in the RESET mode. When incoming MIDI clock is detected, only a single press of the TAP button is required. The loop size is automatically calculated based on the tempo of the incoming MIDI clock and the number of beats selected on the front panel.
There is a way of disabling JamMan's auto-detect mode but you can only do it via the diagnostics and it must be done every time the system is power cycled. This has been addressed in a "Disable MIDI Clock In" app note.