Date   : Fri, 13 Apr 2001 14:47:03 -0000
From   : "Tom Walker" <tommowalker@...>
Subject: BBC CRTC and ACIA

I've got a couple of questions regarding the 6845 CRTC :

1. Do any registers control the total number of scanlines in a frame (ie 312 
for PAL, 262 for NTSC)?
2. What is the exact function of R5 (vertical adjust)?

Also, what happens when the ACIA receives data, or a carrier? How does the 
BBC use these interrupts for tape input? Also, what or the OSFSC and OSFILE 
entry points for the US BBC OS?
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