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archive:computers:colors.32k

> 32,768 Colors! STR Feature Just keep on ..keeping on…….

 ==========================
                 32,768 Color Support for the Atari ST

by Barry Orlando

Public Domain, Dated 09-09-89

   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 List
                              ==========
    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
   To be  used with  this modification  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.

  • *
  • Color Board Layout *
  • *
  • |———– 2 1/2" ————-| *
  • _ *
  • | | | *
  • | || | | -==- | | || *
  • | || S | | -==- | | S || *
  • | || H | | -==- | | H || *
  • | || I | | -==- | | I || *
  • | || F | | -==- | | F || *
  • | || T | | -==- | | T || *
  • | || E | | -==- | | E || *
  • | || R | | -==- | | R || *
  • | || | | -==- | | || *
  • || 1 | | -==- | | 2 || *
  • 3 1/2" || | | -==- | | || *
  • || | | -==- | | || *
  • | || *| | -==- | | *|| *
  • | ||| | -==- | ||| *
  • | | <> <> <> | *
  • | | | *
  • | | <> |* | <> ←—–decoupling caps. *
  • | | | | | *
  • | | |* | | | |* | | *
  • | | | | | | | | | *
  • | | ()| | [] | | [] | | | *
  • | | ()| | | | ^ | | | *
  • | | ()| | | | | | |←—— 74HC243N *
  • | | || || | || | *
  • _|_ |_^_^_|| *
  • | | |_ 3.0K ohm resistors *
  • 74HC00N | |___ 74HC245N *
  • *
  • *
  • *
/data/webs/external/dokuwiki/data/pages/archive/computers/colors.32k.txt · Last modified: 1999/10/13 05:31 by 127.0.0.1

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