Re: IIe double modes

[Mike Pfaiffer <pfaiffer@mbnet.mb.ca>]

Jonathan Schattke wrote:
> 
> I got a second-run //e to help me verify AppleWin's functionality, and
> one of the first things I did was to check out the Double-Hires &
> double-LoRes graphics.

	What ia AppleWin?

> The following anomalies occurred:
> 
> If I turn on AN3 with poke-16290,0 and have the machine in 40-column
> mode, Lo-Res mode is 40x40, but the colors are as if the screen was
> directly mapped to hi-res.

	As I recall it you should activate the 80 column card first. If the
card is active you can switch back and forth between 40 and 80 columns.
This will correspond to a 40 or 80 column grahics screen. If the 80
column card is inactive you should only be able at access a 40x40 lores
screen.

	As an aside you can get an extra 8 lines of vertical resolution by
shutting off the text. Also there is some support in Applesoft for
double lores.

> If I then turn on 80-column mode, the lores is 80x40, but the colors for
> the aux bank pixels are mixed up, 0,8,1,9,2,10,3,11,4,12,5,13,6,14,7,15
> corresponding to 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,and 15.

	Without checking out everything it looks like the colour values are
rotated right by one pixel. Since each byte controls two pixels try
doing a direct poke into the text page and see what happens. This way
you can see what's up.
 
> Also, I seem to get slightly different colors in DHR mode: 32 of them (I
> guess this is because a DHR pixel is half a pixel).

	Think in binary. The HGR pixels (monochrome) are of the form P654 3210.
The P is used if you want colour in which case the pixels would look
like this... P322 1100. Pixel 3 would span two bytes. Here the P bit
allows a choice of colours from two pallets. Functionally because
pattern 00 is black for both pallets and 11 is white for both the only
real change would be for the pixel patterns 01 and 10. This means you
can get strange effects when you place one pixel next to another.

	For DHGR the process is similar in as much as the storage of pixels in
monochrome mode are identical. The exception is the first set of pixels
is stored in the AUX bank where as the next byte takes place in the MAIN
bank.

	Colour DHGR is interesting. Each pixel is made up of four bits stored
almost as you would expect. Here is what I mean with the first byte in
the AUX bank and the second byte in the MAIN bank. P111 0000 P332 2221.
Assuming the pallet bit remains the same the result should be sixteen
colours. Here is the REALLY interesting bit... Are the colours the same
if you change the pallet? If so, you could end up with 30 colours (black
and white would remain the same for each pallet).
 
> Do these anomalies happen with a IIc or enhanced IIe?

	It should...
 
> I'd really like AppleWin to be 100% accurate.

	What is AppleWin?

				Later
				Mike





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