Arty computers

[Chuck Guzis]

On 4 Feb 2007 at 20:11, Tony Duell wrote:

> In which case simply counting M1s won't tell you how many instructions 
> have bene exectued (assuming yopu could an LDIR as 1 instruciton, no 
> matter how many times it repeats).

Now we're splitting hairs.  Functionally, there's not a whole lot of 
difference between LDIR and

    L1:
      LDI
      DJNZ L1

The Z80 enters an M1 state for every repetition.  I suspect (but 
haven't verified it) that if the LDIR modifies itself, the modified 
code executes on the next M1 cycle (i.e. the CPU remembers nothing 
from one iteration to the next).

Didn't the GI CP1600 have an external line that, if activated, would 
inhibit P-counter increment?  I don't know if anyone ever used it for 
anything.

Cheers,
Chuck