Ben Eater 6502 Kit — Day 10 – Attach ROM to CPU
After I checked the CPU by hardcoding a NOP
operation with 8 1kΩ resistors the next step is adding a ROM to for the
future programs. Or better an EEPROM (electrical erasable read only memory). I already filled the ROM with NOP
in Ben
Eater 6502 Kit — Day 8. All I need to do is attach
the ROM. Which is quite a bit of work:
All memory added to a computer need a memory management unit to generate the chip select signals o the correct chip is activated. This project uses a simple 4×2 NAND to do the job. Mind you, I have an 2×4 AND and 1×8 NAND as well to make it more sophisticated.
The placement of the address lines on the AT28C256 is rather chaotic.
After attaching the ROM I tested the CPU. The result was as expected: After the reset sequence the CPU started execution at EAEA₁₆ as described in the video.
You find the full source code with makefiles, project files and everything on GitLab: 6502Tutorial — Tools/Create_NOP