Was kann ein ST mit dem Ding da denn anstellen?Farbpalette stark erweitert und Anzahl gleichzeitig darstellbarer Farben vermutlich auch. Benötigt aber spezielle Programmierung IIRC. M.E. überflüssig, da das Dingen eh keiner hat und auch keine SW im Umlauf zu sein scheint, die das ausnutzt. Auflösung wird aber nicht erhöht.
32,768 Color Support for the Atari ST
by Barry Orlando
for Public Domain, dated 9-9-89
Here's a hardware modification for the standard Atari ST that increases
the color palette from 512 colors to 32,768 colors (32 shades of gray), while
still maintaining compatibility with existing Atari ST software (including
SPECTRUM 512). It is software compatible with the JRI's 4096C color board and
will also be compatible with the recently announced 4096 color STE (enhanced
ST).
It does this by adding increased bits of resolution so as to increase the
ST's 16 read/write colors palette hardware registers from their standard 9
bits each, to 15 bits each. Each of the standard color palette registers have
the following bit arrangement:
FEDCBA9876543210
.....RRR.GGG.BBB
where, R, G, and B are the red, green, and blue components.
The higher the value for any of these grouped bits, the more intense the
resulting color component. The above bits marked '.' are ignored.
The JRI 4096C color board and the upcoming 4096 color STE add an extra bit
of resolution at bit locations 3, 7, and B, however these new bits are least
significant bits so as to maintain compatibility with existing software.
The 32,768 color modification goes a step further by adding a fifth (and
less significant) bit to each color component at locations C, D, and E. The
new arrangement is then:
FEDCBA9876543210
.RGBRRRRGGGGBBBB
As with the JRI 4096C color board, this modification adds an additional
Shifter chip. However this modification is slightly more involved in that it
uses three additional integrated circuits, and bypasses 9, 5% tolerance
resistors used by the Shifter chip, in favor of using 9, 1% tolerance
resistors.
Disclaimer of Liability
This modification should not be attempted by anyone except by someone with
experience repairing or building digital electronic circuits. Performing this
modification will be done at your own risk and may void the warranty on your
computer.
Parts Used
Qty Description/Source/Cost
1 Component Perfboard (3" x 2.5") cut from Radio Shack #276-147
($2.99).
2 3M Board Mounting Interconnectors (straight single-row
male).Digi-Key Part # 929834-08-36 ($2.05 each).
Digi-Key Corp.
701 Brooks Ave South
P.O Box 677
Thief River Falls, MN 56701-0677
Phone 1-800-344-4539 for free catalog.
1 Quad 2 input NAND Gate, High Speed CMOS (74HC00N). Digi-Key
Corp., Part # MM74HC00N ($0.28).
1 Quad Tri-State Transceiver, High Speed CMOS (74HC243N). Digi-Key
Corp., Part # MM74HC243N ($0.78).
1 Octal Tri-State Transceiver, High Speed CMOS (74HC245N).
Digi-Key Corp., Part # MM74HC245N ($0.82).
5 each 3.76K, 7.50K, 15.0K, 30.1K, 60.4K ohm metal film resistors, 1%,
1/4 watt. Digi-Key Corp., Part #s 3.76X, 7.50X, 15.0X, 30.1X,
60.4X (each value: 5 for $0.50)
2 3.0K ohm carbon resistors, 5%, 1/4 watt. Digi-Key Corp., Part #
3.0E (5 for $0.25)
5 0.1ufd Monolithic Ceramic capacitors, Radial, 50V, 10%, or
equivalent substitution, Digi-Key Corp. Part # P4525 ($0.19
each)
2 Shifter Chip, Atari Part # CO25914-38A, one chip is obtained
from your ST's motherboard, the other from your local Atari
Authorized Service Center ($30.00)
Installation of the Board
Located on the ST's motherboard is mounted a sheet metal box which houses
the Shifter Chip. This box has a hinged lid which can be opened. Inside this
box you'll find the Shifter Chip mounted in a 40 pin socket.
The board simply plugs into this socket so that the board is elevated
above the ST's motherboard with sufficient clearance to allow closing the
hinged lid.
Three wires are installed from the color board to three vias (trace thru
holes) located nearby on the motherboard.
Additionally, jumpers are installed across each of three 3.6K ohm
resistors on the motherboard. These resistors are easily traced from the
Shifter socket pins 21, 24, and 27.
Circuit Schematic
I was going to get the circuit diagram for this project digitized, but
just didn't get around to it (saved you the download). So if you want it send
me a self addressed stamped envelope to the following address:
Barry Orlando
1120 Deerfield Dr.
Napa, CA 94558
Board Assembly
Because the sheet metal box (discussed above) does not allow alot of head
clearance, all components are mounted directly to the perfboard. If you use
chip sockets, the hinged lid will not fit back on without modification.
The diagram below shows the orientation of components. I soldered all the
components to the perfboard then soldered all the connections using 30 gauge
Kynar wire wrap solid conductor wire (Radio Shack 278-502).
There is a slight modification to the circuit if you have any RAM chips
installed in your ST which are 150 nanosecond (i.e., slower than 120
nanosecond). Pin 1 (DIR) of the 74HC245N must be tided to ground instead of
to the R/W line on Shifter. This will only disable the read capability for
bits C, D, and E of each color palette register mentioned above.
Software
Included with this text file is a program to display all gray levels and
colors. This is a very crude program but was intended to only prove that the
circuit works. I have also included the C source code which provides the
engine for converting basic color intensities to board compatible bit
patterns.