BBC Model B - video help

From: Andrew Davie <adavie_at_mad.scientist.com>
Date: Wed Feb 25 05:34:06 1998

>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
Received on Wed Feb 25 1998 - 05:34:06 GMT