Anyone know how the BASIC ROM works?
- Hi everybody,
My Tutor emulator is faring quite nicely - I now have the graphic
editor working fine (at last) but am quite stumped when going into the
Assuming the ROM dump I have is correct (and it seems ok), there is a
routine which takes commands from R11 (the program counter after
calling the routine in other words) and then parameters if necessary
from after that. The routine then appears to do various things
according to the command before looping back round again. The loop
appears to be begin at >5380.
The problem is the "command" with the value F322 - it seems invalid,
but it appears in a place which looks good (directly after a valid
command) and is repeated with a different operand. The problem is that
the routine takes a jump address from the (command & >01e0) >> 5 added
to a lookup table at >584c. This would be great but F322 & 01E0 = 0110
and 0110 >> 5 is 3 - which is ODD! Not surprisingly this jumps
merrily into the location straddling two routines in the lookup table,
and gets lost by jumping to >6855.
Does anyone here have any idea what's going on? Has anybody tried to
understand the ROM before me? I've got a pretty good idea about how
most of it works now, but I can`t figure this out yet.
Thanks for any help! If anyone wants I can send them my source code
to have a look at...
- Sure, send it along and I'll look at it and steal it! It's what I do
best! Ha ha ha ha ha!
emucompboy ATnospam yahoo DOTnospam COMnospam
--- In email@example.com, "spirantho" <IanG@a...> wrote:
> Thanks for any help! If anyone wants I can send them my source
> to have a look at...