Re: Create Text & High Resolution into Screen

[Eric Smith <eric-no-spam-for-me@brouhaha.com>]

<BPARKOFF4@satx.rr.com> writes:
>     I understand that every 6502's half cycle reads $400-$7FF for Text Mode
> and $2000-$3FFF for HGR Mode before second half cycle paints 14 pixels to
> the screen.  I think that Text Mode has to paint 56 pixels (7x8) to the
> screen each Text character during every second half cycle, but only 14
> pixels will be painted for HGR Mode.

No.  In text mode, during each video cycle, one character is fetched from
RAM, and the character code and the scan line within the character (zero
for the top line through seven for the bottom line) are used as inputs to
the character generator (2513 in early models, a normal 2K*8 ROM in
rev 7 and later).

Each line of text takes 8 scan lines of 65 clocks each (520 total).  On
each scan line, 40 of the RAM cycles are used to read the actual text.
The remaining RAM cycles (25 per scan line) fetch data that is not
displayed, and serve only to perform RAM refresh.