Raspberry PI Pico(W) - 6502 microprocessor ROM emulator

This is a simple ROM emulator for the 6502 microprocessor using the Raspberry PI Pico. The emulator can be used to test the 6502 microprocessor without the need for a physical ROM/EEPROM chip. The emulator can be used to test the 6502 microprocessor with a clock frequency of up to 1Mhz.

The entire 6502 build and examples is inspired by Ben Eater's 6502 computer build

Requirements

• ARM toolchain
• GCC
• CMake
• Python
• Raspberry PI Pico SDK
• VASM Old-style assembler Download Here
• XXD (For converting binary to C header file)

GPIO Assignments

• PIN 0-15: Address Bus (A0-A15)
• PIN 16-22, 26: Data Bus (D7-D0)
• PIN 27: Read/Write (R/W)
• PIN 28: Clock (From the clock/timer)

Generating the ROM

Using the vasm assembler makerom.sh <assembly_file>

The second way is to use the vasm assembler to generate the ROM. The makerom.sh script assembles the given assembly file and generates a binary file. The binary file is then converted to a C header file using the xxd command. Make sure to add the .section code, "rx" directive to the start of your assembly files to make sure that the code is placed in the correct section of the binary file.

Building and Flashing

[makerom.sh <assembly_file>] && ./upload.sh

Make sure that the Pico is in BOOTSEL mode before running the script.

Working with RAM (6502 Stack R/W)

To avoid conflicts with an external RAM a ROM_STACK_START=0x0000 and ROM_STACK_END=0x07FF is defined in the CMakeLists.txt file. The ROM will set the data pins to high impedance when the address is within this stack range to avoid bus contention.