71 lines
2 KiB
Markdown
71 lines
2 KiB
Markdown
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# AT27C040 PLCC to Commodore PET/CBM ROM Adapter PCB
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* Emulate 4K or 2K ROM
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* Up to 16 different images on one ROM, selectable with 4 DIP switches
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* Can be produced 1-sided (but then only 4 different images can be used)
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## Variations
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* 4K vs 2K
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* 4K: Leave center solder bridge uncut
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* 2K: Cut center solder bridge
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* Configuration
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* unconfigurable
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* Leave all solder bridges
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* Do not populate the pullup resistors
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* 1-sided, 2-bit configurable
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* Cut the solder bridges beneath the dip switches
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* Populate the pullup resistors on the front side
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* 2-sided, 4-bit configurable
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* Cut the solder bridges beneath the dip switches and on the bacl side
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* Populate the pullup resistors on both sides
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## Image Generation
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Use `./mk27c040.py` to generate one 512K image from multiple individual 4K oder 2K images, e.g.:
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```
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./mk27c040.py -o combined.bin --00000 image1.bin --20000 image2.bin
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```
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You can look up the base addresses for the different DIP switch positions in the tables below.
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When the output image has been created, you can flash it to the ROM chip (using `minipro` in this example):
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```
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minipro -p AT27C040@PLCC32 -w combined.bin
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```
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### DIP Switch to Base Address Mapping
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When only 2 and 3 are populated:
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| 2 | 3 | Base Address |
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|---|---|--------------|
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| 0 | 0 | `$09000` |
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| 0 | 1 | `$01000` |
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| 1 | 0 | `$08000` |
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| 1 | 1 | `$00000` |
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When all 4 switches are populated:
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| 1 | 2 | 3 | 4 | Base Address |
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|---|---|---|---|--------------|
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| 0 | 0 | 0 | 0 | `$39000` |
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| 0 | 0 | 0 | 1 | `$19000` |
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| 0 | 0 | 1 | 0 | `$31000` |
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| 0 | 0 | 1 | 1 | `$11000` |
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| 0 | 1 | 0 | 0 | `$38000` |
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| 0 | 1 | 0 | 1 | `$18000` |
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| 0 | 1 | 1 | 0 | `$30000` |
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| 0 | 1 | 1 | 1 | `$10000` |
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| 1 | 0 | 0 | 0 | `$29000` |
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| 1 | 0 | 0 | 1 | `$09000` |
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| 1 | 0 | 1 | 0 | `$21000` |
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| 1 | 0 | 1 | 1 | `$01000` |
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| 1 | 1 | 0 | 0 | `$28000` |
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| 1 | 1 | 0 | 1 | `$08000` |
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| 1 | 1 | 1 | 0 | `$20000` |
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| 1 | 1 | 1 | 1 | `$00000` |
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