[Simh] pdp7/decsys bug?

[Robert Armstrong]

> On the other hand, TSS/8 seems to be calling unimplemented 
> instructions all the time. It stopped almost as soon as I ran
> it with the above instruction. 

  TSS/8 uses unimplemented IOTs (i.e. 06xxx opcodes) as monitor calls.  With
the PDP-8 User Mode flag set, _all_ IOTs trap to the OS whether the hardware
actually implements them or not, and the TSS/8 designers simply picked some
unimplemented IOTs as the official way to call monitor functions.  Is that
what you're seeing??

Bob Armstrong