[Coco] Assembly help: Corrupted bin file ?

[Ciaran Anscomb]

"Fedor Steeman" wrote:
> 
> ffc6/ffc7 SAM Display Offset bit F0
> ffc8/ffc9 SAM Display Offset bit F1
> ffca/ffcb SAM Display Offset bit F2
> 
> What exactly is meant with offset and why must it be set three places?
> Thanks for any hints. I am aware that I must strik you all as a bit
> clueless. :-)

You're adjusting the display offset in the SAM's configuration register.
Because the SAM isn't connected to the data bus, it doesn't get to
see any value you write, just that you wrote to a particular place, so
there's a big block of special addresses it knows about that sets and
resets individual bits in the register.

In this case, you're adjusting the part of the register that controls the
display offset, setting bits 0-2 which (assuming the rest are cleared)
results in 7.  This multiplied by 512 leads to a video display offset
of 3584, or $0E00.

..ciaran
-- 
Ciaran Anscomb, Perl/C Hacker