6502_emulator

Projects:

You can find 3 projects.

1. 6502_lib is 6502 cpu implementation. You can grab this project and include it into your project and use the cpu.
2. 6502_test is Google Test project containing tests for each cpu instructions
3. 6502_emulator is simple code runner showing example how to use cpu.

Compilation:

To compile this project you need to have CMake and MinGw installed.

Usage:

In project 6502_emulator you can find main.cpp file. In this file you can write program by filing byte array called program.

First two bytes of the program contains memory location where program will be placed. Program is loaded by static method CPU::LoadProgram(Bus &memory, const uint8_t *program, uint8_t programSize)

Simple program:

; assembly 
            * = #0x8000         ; tells cpu where the program is located at the memory
            
                   ;set value in memory which will be later loaded into A register
                LDY 0x15       ; {instruction at 0x8000}   load value into Y register
                STY #0x4312    ; {instruction at 0x8002}   store X register into 0x4312
     
                   ;set LSB for indirect address
                LDX 0x12       ; {instruction at 0x8005}   load 0x12 into X register
                STX 0x23       ; {instruction at 0x8007}   store X register into 0x23
     
                   ;set MSB for indirect address
                LDX 0x43       ; {instruction at 0x8009}   load 0x43 into X register
                STX 0x24       ; {instruction at 0x800B}   store X register int 0x24
     
                   ;indirect address is now stored at 2 cells: 0x23 (LSB) and 0x24 (MSB)
                   ; load indirect address into A register
                LDX 0x13       ; {instruction at 0x800D}   load 0x13 into X register - offset for zero-page address
                LDA ($0x10, X) ; {instruction at 0x800F}   load Accumulator from indirect address X(0x13) + 0x10 -> 0x0023 and 0x0024

//first two bytes tells where the program will be placed
program[0] = 0x00;
program[1] = 0x80;

//set value in memory which will be later loaded into A register
program[2] = INSTRUCTIONS::INS_LDY_IM; // 2 cycles
program[3] = 0x15; //this value will be stored in ACC register by indirect address
program[4] = INSTRUCTIONS::INS_STY_ABS; //4 cycles
program[5] = 0x12;
program[6] = 0x43; //Y register will be stored at 0x4312

//set LSB for indirect address
program[7] = INSTRUCTIONS::INS_LDX_IM; // 2 cycles
program[8] = 0x12;     //set  LSB
program[9] = INSTRUCTIONS::INS_STX_ZP;  //3 cycles
program[10] = 0x23;    //store LSB in 0x22

//set MSB for indirect address
program[11] = INSTRUCTIONS::INS_LDX_IM; // 2 cycles
program[12] = 0x43;     //set  MSB
program[13] = INSTRUCTIONS::INS_STX_ZP; //3 cycles
program[14] = 0x24;    //store MSB in 0x23

//now mem[0x0023] = 0x12 (LSB) and mem[0x0024] = 0x43 (MSB)

//load indirect address into A register
program[15] = INSTRUCTIONS::INS_LDX_IM; // 2 cycles
program[16] = 0x13; //zero-page offset
program[17] = INSTRUCTIONS::INS_LDA_IND_X; // 6 cycles
program[18] = 0x10; // zero-page address for indirect address
                    // - address for A register will be read from 0x10+0x13