25 Feb
1998
25 Feb
'98
5:34 a.m.
Firstly, does Mode 7 behave correctly? Not only does it
have the simplest
mapping, it also uses different address buffers between the 6845 CRTC
chip and the RAM. On my diagram, IC10 and IC11 are used in Mode7. IC8
and IC9 are used in all the other modes. So if _all_ modes, including
Mode7 are faulty, then it's unlikely to be a buffer problem.
Mode 7 behaves as my earlier email. Basic repeat unit 64. Mode 0 behaves
as if we had two mode 7 screens - and the repeat unit and behaviour
unchanged. That would make it unlikely to be a buffer problem, by your
reckoning.
Secondly, go into mode 0, and count the number of
characters until it
repeats. Multiply that by 8 (to get the the number of bytes before it
repeats) and that'll tell you which address line to look at.
Well, 64 characters. That would make it.... 256 bytes, no?
Therefore, (guessing) um.... address line 8 (I start counting at 0).
SO... uh.... where?
Sorry I'm such an electronic idiot.
A