4 Feb
2007
4 Feb
'07
2:56 p.m.
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