Re: What is this graphics mode called?

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

David Empson <dempson@actrix.gen.nz> wrote:

> 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.)

Hang on, I'm getting my groups of soft switches mixed up. LORES is
$C056.

$C05E is one of the soft switches for Annunciator 3, which is used to
turn on double hi-res graphics mode.

I can see that it changing colours in 40-column lo-res mode, so this is
probably an artifact of the IIe graphics hardware, not an officially
defined mode.

The IIgs (Mega II chip) does it as well.

> 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