When building the MPG-200 for the JX-3P, I discovered that the busy line is hardwired via a pullup resistor to +5V, in effect tying it to logic high.
Because of this, I decided to ignore it altogether. But when trying to get the MPG-200 to work with the MKS-30, I discovered that this synth actually DO control the line.
So what actually happens when the busy line is pulled low?
As expected, the PG-200 does not transmit anything while the line is low. Still, I was curious what happened afterwards, when the line was released again - did the PG-200 just ignore whatever had happened during busy, did it queue up events or did it send the new stable status?
Well, a bit of both really. It keeps the last state from before it was blocked. Then, once busy is cleared, it sends first the state it had before blocking, and then the state after blocking. This happens for both switches and potentiometers.