6502 Emulator

This repository contains the source code for a 6502 Emulator, written in C++. The emulator is designed to replicate the functionality of the 6502 microprocessor, which was widely used in early personal computers.

The 6502 emulator is provided as a static library that can be plugged into any frontend. The main API provides the following function:

• emulator::execute(cpu, program) that takes an entire program and the initialised Cpu struct, and then executes the whole program, changing the state of the given Cpu as expected.
• emulator::execute_next(cpu, program) single steps the next isntruction on the given cpu.

Getting Started

To get started with the 65k-cpp emulator, clone the repository and follow the instructions below:

The tools needed to build are:

• cmake version 3.28 or above.
• ninja version 1.11 or above.

git clone https://github.com/matheusgomes28/65k-cpp.git
cmake --preset unix-rel-ninja
cmake --build --preset unit-rel-ninja

Plans

The goal for this project is to have support for all opcodes in ths standard 6502.

In addition, the aim to to provide a couple of front end applications that can step through 6504 applications, showing state of flags, registers, and memory:

Opcode support

This section contains support tables for each operation. The tickbox in the supported column indicates whether or not the operation is isupported.

• ✅ means opcode support and tests are available.
• 🆗 means opcode support is available, but tests needs writing.
• ❌ means there's no opcode support or tests.

AND - And Memory with Accumulator

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
AND	Immediate	0x29	2	2	✅
AND	Zero Page	0x25	2	3	✅
AND	Zero Page, X	0x35	2	4	✅
AND	Absolute	0x2D	3	4	✅
AND	Absolute, X	0x3D	3	4*	✅
AND	Absolute, Y	0x39	3	4*	✅
AND	(Indirect, X)	0x21	2	6	✅
AND	(Indirect), Y	0x31	2	5*	✅

Total number of AND instructions: 8

EOR - Exclusive-Or Memory with Accumulator

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
EOR	Immediate	0x49	2	2	✅
EOR	Zero Page	0x45	2	3	✅
EOR	Zero Page, X	0x55	2	4	✅
EOR	Absolute	0x4D	3	4	✅
EOR	Absolute, X	0x5D	3	4*	✅
EOR	Absolute, Y	0x59	3	4*	✅
EOR	(Indirect, X)	0x41	2	6	✅
EOR	(Indirect), Y	0x51	2	5*	✅

Total number of EOR instructions: 8

ORA - Or Memory with Accumulator

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
ORA	Immediate	0x09	2	2	✅
ORA	Zero Page	0x05	2	3	✅
ORA	Zero Page, X	0x15	2	4	✅
ORA	Absolute	0x0D	3	4	✅
ORA	Absolute, X	0x1D	3	4*	✅
ORA	Absolute, Y	0x19	3	4*	✅
ORA	(Indirect, X)	0x01	2	6	✅
ORA	(Indirect), Y	0x11	2	5*	✅

Total number of ORA instructions: 8.

LDA - Load Accumulator with Memory

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
LDA	Immediate	0xA9	2	2	✅
LDA	Zero Page	0xA5	2	3	✅
LDA	Zero Page, X	0xB5	2	4	✅
LDA	Absolute	0xAD	3	4	✅
LDA	Absolute, X	0xBD	3	4*	✅
LDA	Absolute, Y	0xB9	3	4*	✅
LDA	(Indirect, X)	0xA1	2	6	✅
LDA	(Indirect), Y	0xB1	2	5*	✅

Total number of LDA instructions: 8.

LDX - Load X Register with Memory

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
LDX	Immediate	0xA2	2	2	✅
LDX	Zero Page	0xA6	2	3	✅
LDX	Zero Page, Y	0xB6	2	4	✅
LDX	Absolute	0xAE	3	4	✅
LDX	Absolute, Y	0xBE	3	4*	✅

Total number of LDX instructions: 5.

LDY - Load X Register with Memory

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
LDY	Immediate	0xA0	2	2	✅
LDY	Zero Page	0xA4	2	3	✅
LDY	Zero Page, Y	0xB4	2	4	✅
LDY	Absolute	0xAC	3	4	✅
LDY	Absolute, Y	0xBC	3	4*	✅

Total number of LDY instructions: 5.

LDY - Load Y Register with Memory

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
LDY	Immediate	0xA0	2	2	✅
LDY	Zero Page	0xA4	2	3	✅
LDY	Zero Page, Y	0xB4	2	4	✅
LDY	Absolute	0xAC	3	4	✅
LDY	Absolute, Y	0xBC	3	4*	✅

Total number of LDY instructions: 5.

STA - Store Accumulator in Memory

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
STA	Zero Page	0x85	2	3	✅
STA	Zero Page, X	0x95	2	4	✅
STA	Absolute	0x8D	3	4	✅
STA	Absolute, X	0x9D	3	5	✅
STA	Absolute, Y	0x99	3	5	✅
STA	(Indirect, X)	0x81	2	6	✅
STA	(Indirect), Y	0x91	2	6	✅

Total number of STA instructions: 7.

STX - Store Accumulator in Memory

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
STX	Zero Page	0x86	2	3	✅
STX	Zero Page, Y	0x96	2	4	✅
STX	Absolute	0x8E	3	4	✅

Total number of STX instructions: 3.

STY - Store Accumulator in Memory

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
STY	Zero Page	0x84	2	3	✅
STY	Zero Page, Y	0x94	2	4	✅
STY	Absolute	0x8C	3	4	✅

Total number of STY instructions: 3.

Transfer Operations

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
TAX	Implied	0xAA	1	2	✅
TAY	Implied	0xA8	1	2	✅
TSX	Implied	0xBA	1	2	✅
TXA	Implied	0x8A	1	2	✅
TXS	Implied	0x9A	1	2	✅
TYA	Implied	0x98	1	2	✅

Total number of transfer instructions: 6.

Stack Operations

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
PHA	Implied	0x48	1	3	✅
PHP	Implied	0x08	1	3	✅
PLA	Implied	0x68	1	4	✅
PLP	Implied	0x28	1	4	✅

Total number of stack instructions: 4.

Decrement and Increment Operations

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
DEC	Zero Page	0xC6	2	5	✅
DEC	Zero Page, X	0xD6	2	6	🆗
DEC	Absolute	0xCE	3	6	🆗
DEC	Absolute, X	0xDE	3	7	🆗
DEX	Implied	0xCA	1	2	✅
DEY	Implied	0x88	1	2	✅
INC	Zero Page	0xE6	2	5	✅
INC	Zero Page, X	0xF6	2	6	✅
INC	Absolute	0xEE	3	6	✅
INC	Absolute, X	0xFE	3	7	✅
INX	Implied	0xE8	1	2	✅
INY	Implied	0xC8	1	2	✅

Total number of stack instructions: 12.

ADC - Add to Accumulator with Carry

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
ADC	Immediate	0x69	2	2	❌
ADC	Zero Page	0x65	2	3	❌
ADC	Zero Page, X	0x75	2	4	❌
ADC	Absolute	0x6D	3	4	❌
ADC	Absolute, X	0x7D	3	4*	❌
ADC	Absolute, Y	0x79	3	4*	❌
ADC	(Indirect, X)	0x61	2	6	❌
ADC	(Indirect), Y	0x71	2	5*	❌

Total number of ADC instructions: 8.

SBC - Subtract Memory from Accumulator with Borrow

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
SBC	Immediate	0xE9	2	2	❌
SBC	Zero Page	0xE5	2	3	❌
SBC	Zero Page, X	0xF5	2	4	❌
SBC	Absolute	0xED	3	4	❌
SBC	Absolute, X	0xFD	3	4*	❌
SBC	Absolute, Y	0xF9	3	4*	❌
SBC	(Indirect, X)	0xE1	2	6	❌
SBC	(Indirect), Y	0xF1	2	5*	❌

Total number of SBC instructions: 8.

ASL - Shift Left One Bit

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
ASL	Accumulator	0x0A	1	2	✅
ASL	Zero Page	0x06	2	5	✅
ASL	Zero Page, X	0x16	2	6	✅
ASL	Absolute	0x0E	3	6	✅
ASL	Absolute, X	0x1E	3	7	✅

Total number of ASL instructions: 5.

LSR - Shift Right One Bit

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
LSR	Accumulator	0x4A	1	2	✅
LSR	Zero Page	0x46	2	5	✅
LSR	Zero Page, X	0x56	2	6	✅
LSR	Absolute	0x4E	3	6	✅
LSR	Absolute, X	0x5E	3	7	✅

Total number of LSR instructions: 5.

ROR - Rotate Right One Bit with Carry

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
ROR	Accumulator	0x6A	1	2	✅
ROR	Zero Page	0x66	2	5	✅
ROR	Zero Page, X	0x76	2	6	✅
ROR	Absolute	0x6E	3	6	✅
ROR	Absolute, X	0x7E	3	7	✅

Total number of ROR instructions: 5.

ROL - Rotate Left One Bit with Carry

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
ROL	Accumulator	0x6A	1	2	✅
ROL	Zero Page	0x66	2	5	✅
ROL	Zero Page, X	0x76	2	6	✅
ROL	Absolute	0x6E	3	6	✅
ROL	Absolute, X	0x7E	3	7	✅

Total number of ROL instructions: 5.

CMP - Compare Memory with Accumulator

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
CMP	Immediate	0xC9	2	2	✅
CMP	Zero Page	0xC5	2	3	✅
CMP	Zero Page, X	0xD5	2	4	✅
CMP	Absolute	0xCD	3	4	✅
CMP	Absolute, X	0xDD	3	4*	✅
CMP	Absolute, Y	0xD9	3	4*	✅
CMP	(Indirect, X)	0xC1	2	6	✅
CMP	(Indirect), Y	0xD1	2	5*	✅

Total number of CMP instructions: 8.

CPX - Compare Memory with X Register

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
CPX	Immediate	0xE0	2	2	✅
CPX	Zero Page	0xE4	2	3	✅
CPX	Absolute	0xEC	3	4	✅

Total number of CPX instructions: 3.

CPY - Compare Memory with Y Register

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
CPY	Immediate	0xC0	2	2	✅
CPY	Zero Page	0xC4	2	3	✅
CPY	Absolute	0xCC	3	4	✅

Total number of CPY instructions: 3.

Flag Operations

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
CLC	Implied	0x18	1	2	✅
CLD	Implied	0xD8	1	2	✅
CLI	Implied	0x58	1	2	✅
CLV	Implied	0xB8	1	2	✅
SEC	Implied	0x38	1	2	✅
SED	Implied	0xF8	1	2	✅
SEI	Implied	0x78	1	2	✅

Total number of flag instructions: 7.

Branching Operations

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
BCC	Relative	0x90	2	2**	✅
BCS	Relative	0xB0	2	2**	✅
BEQ	Relative	0xF0	2	2**	✅
BMI	Relative	0x30	2	2**	✅
BNE	Relative	0xD0	2	2**	✅
BPL	Relative	0x10	2	2**	✅
BVC	Relative	0x50	2	2**	✅
BVS	Relative	0x70	2	2**	✅

Total number of branching instructions: 8.

Jumps and Subroutine Operations

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
JMP	Absolute	0x4C	3	3	✅
JMP	Indirect	0x6C	3	5	🆗
JSR	Absolute	0x20	3	6	❌
RTS	Absolute	0x60	1	6	❌

Total number of jump and subroutine instructions: 4.

Interrupt Operations

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
BRK	Implied	0x00	1	7	❌
RTI	Implied	0x40	1	6	❌

total number of interrupt instructions: 2.

Random Operations

Opcode	Addressing Mode	Opcode (Hex)	Bytes	Cycles	Supported
BIT	Zeropage	0x24	2	3	✅
BIT	Absolute	0x2c	3	4	✅
NOP	Implied	0xEA	1	2	✅

total number of random instructions: 2.

Contributing

Feel free to submit issues or pull requests. Contributions are welcome!

License

This project is licensed under the MIT License.