Re: What is this graphics mode called?

[dempson@actrix.gen.nz (David Empson)]

Sheldon Simms <wsspammy@gmail.com> wrote:

> On 2011-02-10 16:22:12 -0500, Sheppy said:
> 
> > On Feb 10, 3:19 pm, Sheldon Simms <wsspa...@gmail.com> wrote:
> >> The graphics mode I'm curious about is accessed by
> >> 
> >> poke 49246,0
> >> poke 49232,0
> >> 
> >> from reset on a IIe.
> >> 
> >> It seems to be lores, but shifted out at 7 Mhz instead of 14 Mhz.
> >> 
> >> Maybe it could be called extra lo res.
> > 
> > It's called double low-resolution. 
> 
> Really? Then what's the mode called when you do this:
> 
> poke 49246,0
> poke 49165,0
> poke 49232,0

The latter is double lo-res: 80 columns by 48 rows. The extra
soft-switch (49165 = $C00D) is 80VID ON.

The former is standard lo-res: 40 columns by 48 rows. 49246 ($C05E) is
LORES and 49232 ($C050) is GR. (The only other relevant soft-switches
are selecting page1/2 and whether the four rows of text appear at the
bottom.)

Standard lo-res uses a 14 MHz clock to shift out the bit patterns, which
gives it the ability to display 16 colours, but it uses the same
horizontal cell timing as 40-column text, resulting in "short and fat"
blocks.

Double lo-res uses the same 14 MHz clock and same colour set, but
outputs each cell half as long and fetched bytes in parallel from main
and auxiliary memory (like all other 80-column modes), resulting in
twice as many blocks per row, and roughly square blocks.

-- 
David Empson
dempson@actrix.gen.nz