[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Apple //e's RGB Card To Apple IIgs' RGB Monitor
"mdj" <mdj.mdj@gmail.com> wrote in message
1166499011.152258.3620@73g2000cwn.googlegroups.com">news:1166499011.152258.3620@73g2000cwn.googlegroups.com...
>
> Michael J. Mahon wrote:
>
>> I'd suggest using three 4-resistor networks to do the three 4-bit D-to-A
>> conversions--four resistors beats a D/A chip for just 4 bits.
>
> Agreed. It might also be possible nowadays to use a uC to replace the
> GAL idea. GAL/PAL seems to be going the way of the dodo, and using one
> small cheap chip instead of two seems a good move.
>
>> And buffer amplifiers may be needed for the RGB signals as well, if the
>> RGB monitor's inputs are 75 Ohm.
>
> Without this, you'd see some pretty strange colour artifacting.
>
> Also Bryan - your table seems to be quite wrong. Care to post a
> corrected one?
>
> Have you done a comparison of the IIgs's colour palette to the actual
> composite colours? It's possible that 12 bit RGB only provides an
> approximate of some of the colours, although admitedly it's probably
> close enough.
Matt,
Sorry, I made mistake. It should be the correct table to be shown
strange colors below.
IRGB RED GREEN BLUE Hex
Color 0 0000 0000 0000 0000 000
Color 1 0001 0000 0000 1010 00A
Color 2 0010 0000 1010 0000 0A0
Color 3 0011 0000 1010 1010 0AA
Color 4 0100 1010 0000 0000 A00
Color 5 0101 1010 0000 1010 A0A
Color 6 0110 1010 0101 0000 A50
Color 7 0111 1010 1010 1010 AAA
Color 8 1000 0101 0101 0101 555
Color 9 1001 0101 0101 1111 55F
Color A 1010 0101 1111 0101 5F5
Color B 1011 0101 1111 1111 5FF
Color C 1100 1111 0101 0101 F55
Color D 1101 1111 0101 1111 F5F
Color E 1110 1111 1111 0101 FF5
Color F 1111 1111 1111 1111 FFF
This table above is 16 CGA colors. Thanks to Michael's correction when
I made mistake to label RGBI as bit reverse. I believe that RGB, GREEN, and
BLUE data are to be correct because 24 bit data and 12 bit data are 99%
identical when you set "1111" on low nibble or duplicate from high nibble to
low nibble. Filling "1111" on low nibble gives little brightness. You can
use like (12 bit data) A50 as 24 bit data) AA5500 or (24 bit data) AF5F00.
It is how I got 24 bit data information from IBM manufacturer when I
converted from 24 bit to 12 bit to look like Apple IIgs monitor.
I believe that original resistor network use this table above to give
wrong 16 colors to be 16 CGA colors on Apple IIgs' monitor.
I decide not to use 16 CGA color table above. Here is the Apple IIgs'
16 colors table below. Please do not assure if below table is wrong, but I
agree "Color", "RED", "GREEN", and "BLUE" are correct except IRGB. IRGB
will be correct later when it is fixed. The important issue is to use IRGB
from Apple //e's RGB card and translate it into Apple IIgs' 16 colors.
I thought resistor network may give wrong color information. Maybe, you
should use two GAL chips and add resistor network instead of using D/A chip.
GAL chip is like ROM to store Apple IIgs' 16 color table. Two GAL chips
have I signal, R signal, G signal, and B signal as four input from Apple
//e's RGB card and four R signal (4 bits), four G signal (4 bits), and four
B signal (4 bits) as 12 output to resistor network or three D/A chips. Then
resistor network or D/A chip will show correct Apple IIgs' 16 colors, but
not 16 CGA colors.
Is my explanation clear? Please let me know if it is not so clear.
Thanks...
IRGB RED GREEN BLUE Hex
Color 0 0000 0000 0000 0000 000
Color 1 0001 1101 0000 0011 D03
Color 2 0010 0000 0000 1001 009
Color 3 0011 1101 0010 1101 D2D
Color 4 0100 0000 0111 0010 072
Color 5 0101 0101 0101 0101 555
Color 6 0110 0010 0010 1111 22F
Color 7 0111 0110 1010 1111 6AF
Color 8 1000 1000 0101 0000 850
Color 9 1001 1111 0110 0000 F60
Color A 1010 1010 1010 1010 AAA
Color B 1011 1111 1001 1000 F98
Color C 1100 0001 1101 0000 1D0
Color D 1101 1111 1111 0000 FF0
Color E 1110 0100 1111 1001 4F9
Color F 1111 1111 1111 1111 FFF
Bryan Parkoff