> 
> a little off topic, but..
> 
> does anyone have any ideas why when i frob the bits to set status on a 
> TMSCP controller, bad things would happen? it seems that somehow this
> is causing the PSL to get the 'running on interrupt stack' bit set,
> (actually , it is causing a very different psl status to be set)  
>
What happens is that you get an interrupt that changes things.
Note that single-step on the 4000 machines does a "software" single-step
and do not follow interrupts like the 11/750. (It actually sets the
T bit and executes one instruction, just like a debugger).

-- Ragge