Talk to a Texas Instruments TMS9918A video display processor chip via an Arduino Mega clone.
TI, annoyingly, named the least-significant bit (LSB) on its buses "XX0", and the most-significant bit (MSB) "XX7" (or "XX15" if it was a 16-bit bus).
| Arduino pin number | TMS9918A Pin Name | TMS9918A Pin Number |
|---|---|---|
| 51 | !CSW | 14 |
| 2 | CD7 (LSB) | 17 |
| 3 | CD6 | 18 |
| 4 | CD5 | 19 |
| 5 | CD4 | 20 |
| 6 | CD3 | 21 |
| 7 | CD2 | 22 |
| 8 | CD1 | 23 |
| 9 | CD0 (MSB) | 24 |
| GND | Vss | 12 |
Feel free to adapt this sketch to whatever pins you'd like to use. For example, an Arduino Nano is definitely powerful enough to run this sketch -- I simply already owned the Keyestudio Mega 2560 R3 that came with Ben Eater's 6502 kit.
- Use port manipulation instead of bit-twiddling each of the pins
delayMicrosecondsinstead ofdelayfor lower latency- Write to VRAM
- Read from VRAM
- Read status register
- Refactor into a library