What users know about the micro controllers they work with is what the semiconductor companies publish. But the controllers feature a lot more than what can be read in the documentation. There are a some test modes and debug modes that are used during production test and, of course, for emulation. That is why I (being developer at Hitex) know about these modes. Of course, I am not allowed to tell about the modes because we have gotten the information under non-disclosure agreement. But I think I can tell that these modes exist and that the an emulator needs to keep track to the internal execution of the instructions by some synchronisation signals.

An example: Some micros have the possibility to switch ALE off. When such a micro is used for emulation and the instruction that switches ALE off is executed, nothing happens. ALE keeps strobing. The emulator must detect the execution of this particular instruction and must gate the ALE signal on the way from the micro to the target hardware. This can only be done with a little support from the micro. And it requires some signals.

Harald Fluegel