24 Dec
2025
24 Dec
'25
10:43 p.m.
When I did this, I remember there was a pair of registers that I could not save, probably
de. I can look and see if I ended up with useful isr code in my project. Maybe the real
Intended use is to be able to halt and resume on interrupt.
There was a way to cleverly restore the flags.
My isr code is in https://github.com/sbelectronics/h8/blob/master/h8-8008/asm/fpanisr.inc
Sent from my iPhone
On Dec 24, 2025, at 1:02 PM, Robert Armstrong via
cctalk <cctalk(a)classiccmp.org> wrote:
Tom Uban <uban(a)ubanproductions.com> wrote:
Here is the power-up/interrupt code I use on a board I built: ...
Thanks! A couple of questions -
It looks like this code trashes DE, so I assume the background code just can't use
those registers? So there's no way to code a truly transparent ISR?
I also notice that the 8008 lacks any kind of interrupt enable F-F, nor any EI/DI type
instructions. Is that right? I guess you could always implement those with external
hardware, at least.
And the big question - what's your code for restoring these flags when you exit the
ISR? The MCS-8 manual says that all ALU instructions always update all flags, with the
exception of the rotate opcodes which only change carry. It seems that means the ZS&P
flags at least would have to be restored together in one instruction.
Bob