206 lines
9.5 KiB
Plaintext
206 lines
9.5 KiB
Plaintext
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> 32,768 Colors! STR Feature Just keep on ..keeping on.......
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==========================
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32,768 Color Support for the Atari ST
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by Barry Orlando
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Public Domain, Dated 09-09-89
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Here's a hardware modification for the standard Atari ST that
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increases the color palette from 512 colors to 32,768 colors (32 shades of
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gray), while still maintaining compatibility with existing Atari ST
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software (including SPECTRUM 512). It is software compatible with the
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JRI's 4096C color board and will also be compatible with the recently
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announced 4096 color STE (enhanced ST).
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It does this by adding increased bits of resolution so as to increase
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the ST's 16 read/write colors palette hardware registers from their
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standard 9 bits each, to 15 bits each. Each of the standard color palette
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registers have the following bit arrangement:
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FEDCBA9876543210
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.....RRR.GGG.BBB
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where, R, G, and B are the red, green, and blue components.
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The higher the value for any of these grouped bits, the more intense
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the resulting color component. The above bits marked '.' are ignored.
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The JRI 4096C color board and the upcoming 4096 color STE add an extra
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bit of resolution at bit locations 3, 7, and B, however these new bits are
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least significant bits so as to maintain compatibility with existing
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software.
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The 32,768 color modification goes a step further by adding a fifth
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(and less significant) bit to each color component at locations C, D, and
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E. The new arrangement is then:
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FEDCBA9876543210
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.RGBRRRRGGGGBBBB
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As with the JRI 4096C color board, this modification adds an
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additional Shifter chip. However this modification is slightly more
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involved in that it uses three additional integrated circuits, and
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bypasses 9, 5% tolerance resistors used by the Shifter chip, in favor of
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using 9, 1% tolerance resistors.
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Disclaimer of Liability
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This modification should not be attempted by anyone except by someone
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with experience repairing or building digital electronic circuits.
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Performing this modification will be done at your own risk and may void
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the warranty on your computer.
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Parts List
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==========
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Qty Description/Source/Cost
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---------------------------------
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1 Component Perfboard (3" x 2.5") cut from Radio Shack
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#276-147 ($2.99).
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2 3M Board Mounting Interconnectors (straight single-row
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male).Digi-Key Part # 929834-08-36 ($2.05 each).
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Digi-Key Corp.
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701 Brooks Ave South
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P.O Box 677
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Thief River Falls, MN 56701-0677
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Phone 1-800-344-4539 for free catalog.
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1 Quad 2 input NAND Gate, High Speed CMOS (74HC00N). Digi-Key
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Corp., Part # MM74HC00N ($0.28).
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1 Quad Tri-State Transceiver, High Speed CMOS (74HC243N).
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Digi-Key Corp., Part # MM74HC243N ($0.78).
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1 Octal Tri-State Transceiver, High Speed CMOS (74HC245N).
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Digi-Key Corp., Part # MM74HC245N ($0.82).
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5 each 3.76K, 7.50K, 15.0K, 30.1K, 60.4K ohm metal film resistors,
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1%, 1/4 watt. Digi-Key Corp., Part #s 3.76X, 7.50X, 15.0X,
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30.1X, 60.4X (each value: 5 for $0.50)
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2 3.0K ohm carbon resistors, 5%, 1/4 watt. Digi-Key Corp.,
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Part # 3.0E (5 for $0.25)
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5 0.1ufd Monolithic Ceramic capacitors, Radial, 50V, 10%, or
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equivalent substitution, Digi-Key Corp. Part # P4525 ($0.19
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each)
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2 Shifter Chip, Atari Part # CO25914-38A, one chip is
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obtained from your ST's motherboard, the other from your
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local Atari Authorized Service Center ($30.00)
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Installation of the Board
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Located on the ST's motherboard is mounted a sheet metal box which
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houses the Shifter Chip. This box has a hinged lid which can be opened.
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Inside this box you'll find the Shifter Chip mounted in a 40 pin socket.
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The board simply plugs into this socket so that the board is elevated
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above the ST's motherboard with sufficient clearance to allow closing the
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hinged lid.
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Three wires are installed from the color board to three vias (trace
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thru holes) located nearby on the motherboard.
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Additionally, jumpers are installed across each of three 3.6K ohm
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resistors on the motherboard. These resistors are easily traced from the
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Shifter socket pins 21, 24, and 27.
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Circuit Schematic
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I was going to get the circuit diagram for this project digitized, but
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just didn't get around to it (saved you the download). So if you want it
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send me a self addressed stamped envelope to the following address:
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Barry Orlando
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1120 Deerfield Dr.
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Napa, CA 94558
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Board Assembly
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Because the sheet metal box (discussed above) does not allow alot of
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head clearance, all components are mounted directly to the perfboard. If
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you use chip sockets, the hinged lid will not fit back on without
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modification.
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The diagram below shows the orientation of components. I soldered all
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the components to the perfboard then soldered all the connections using 30
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gauge Kynar wire wrap solid conductor wire (Radio Shack 278-502).
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There is a slight modification to the circuit if you have any RAM
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chips installed in your ST which are 150 nanosecond (i.e., slower than 120
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nanosecond). Pin 1 (DIR) of the 74HC245N must be tided to ground instead
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of to the R/W line on Shifter. This will only disable the read capability
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for bits C, D, and E of each color palette register mentioned above.
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Software
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To be used with this modification is a program to display all gray
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levels and colors. This is a very crude program but was intended to only
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prove that the circuit works. I have also included the C source code
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which provides the engine for converting basic color intensities to board
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compatible bit patterns.
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*************************************************************************
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* *
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* Color Board Layout *
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* *
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* |----------- 2 1/2" -------------| *
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* __ ___________________________________ *
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* | | ________ ________ | *
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* | || | | -==- | | || *
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* | || S | | -==- | | S || *
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* | || H | | -==- | | H || *
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* | || I | | -==- | | I || *
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* | || F | | -==- | | F || *
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* | || T | | -==- | | T || *
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* | || E | | -==- | | E || *
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* | || R | | -==- | | R || *
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* | || | | -==- | | || *
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* || 1 | | -==- | | 2 || *
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* 3 1/2" || | | -==- | | || *
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* || | | -==- | | || *
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* | || *| | -==- | | *|| *
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* | ||________| | -==- | |________|| *
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* | | <> <> <> | *
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* | | ____ | *
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* | | <> |* | <> <------decoupling caps. *
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* | | ____ | | ____ | *
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* | | |* | | | |* | | *
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* | | | | | | | | | *
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* | | ()| | [] | | [] | | | *
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* | | ()| | | | ^ | | | *
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* | | ()| | | | | | |<------- 74HC243N *
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* | | |____| |____| | |____| | *
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* _|_ |_____^_________^_____|____________| *
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* | | |_________ 3.0K ohm resistors *
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* 74HC00N ______| |_____ 74HC245N *
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* *
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* *
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* *
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*************************************************************************
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