EaterEmulator - Ben Eater's 8 Bit Breadboard CPU Emulator in Python

EaterEmulator emulates Ben Eater's 8 bit breadboard CPU.

Here's a screenshot

Instruction set

OpCode	Mnemonic	Description
0000	NOP	No Operation
0001	LDA	Load contents of a memory address XXXX into A register
0010	ADD	Load contents of a memory address XXXX into B register, then performs A+B and stores the result in A register
0011	SUB	Load contents of a memory address XXXX into B register, then performs A-B and stores the result in A register
0100	STA	Store contents of A register at memory address XXXX
0101	LDI	Load 4 bit immediate value into A register
0110	JMP	Unconditional jump: sets program counter to XXXX and executes from there
0111	JC	Jump if carry: sets program counter to XXXX when carry flag is set and executes from there
1000	JZ	Jump if zero: sets program counter to XXXX when zero flag is set and executes from there
1110	OUT	Output contents of A register to 7 segment display, in our case, we'll print it on console
1111	HLT	Halts the execution

Implemented Instructions

• NOP
• LDA
• ADD
• SUB
• STA
• LDI
• JMP
• JC
• JZ
• OUT
• HLT

Loading your own program

Loading your own program from .bin file\

Create .asm file and write your assembly program in it. The program should contain atleast 16 lines and each line should consist of 1 or 2 instructions

For example: If you want to write a program that adds 7 and 3 and then subtracts 2 from it, it should something like this

LDA 8
ADD 9
SUB 10
OUT 0
NOP
NOP
NOP
NOP
7
3
2
NOP
NOP
NOP
NOP
NOP

At line 0, we can see LDA 8, this means that, it loads value from address 8 into A register. This address 8 is at line 8 which has a value of 7. So, it Loads 7 into A register.

At line 1, we have ADD 9, this will store contents from address 9 into B register, then adds this value to contents of A register, So, the final value of A register will be 10 and B register will be 3.

At line 2, we have SUB 10, this will store contents from address 10 int B register, then subtracts this value from contents of A register, the final value of A register will be 8 and B register will be 2

At line 3, we have OUT 0, this will OUTPUT the contents of A register on to the console.

Rest of the lines contain NOP instructions.

At line 8, there is 7, this value will be used when line 0 gets executed. At line 9, there is 3, this value will be used when line 1 gets executed. At line 10, there is 2, this value will be used when line 3 gets executed.

In this manner, you have to write your assembly program. And make sure that there are no extra spaces other than spaces between instruction and memory addresses

Once, you write your assembly program, save it. For example, if you have saved it with a name of add.asm, then run the following command to generate .bin file.

eas.py add.asm -o add.bin

This will generate a .bin file. You can run this using the emulator with the following command

cpu.py add.bin 0.05 where 0.05 is the execution speed.

Manually load your own program

Go to cpu.py file in loadProgram() function, add your own program after line 24

For example:

Loading a program that adds 7 and 3 would be as follows

LDA 1000
ADD 1001
OUT 0000

;at address 1000, we'll store 7
;and at address 1001, we'll store 3

In cpu.py file, you should write the code as follows

self.memory[0b0000] = 0b00011000; //LDA 1000 or load 7 into A register from memory[0b1000] or memory[8]
self.memory[0b0001] = 0b00101001; //ADD 1001 or load 3 into B register, then ADD and store it in A
self.memory[0b0010] = 0b11100000; //OUT 0000 or OUTPUT A register contents

//store data in the memory
self.memory[0b1000] = 7; //store 7 at memory[8], so that we can access it using LDA instruction
self.memory[0b1001] = 3; //store 3 at memory[9], so that we can access it using ADD instruction

You can write numbers in binary format or hexadecimal format

Here's a program that prints Triangular numbers upto 255,

self.memory[0x0] = 0x1F
self.memory[0x1] = 0x2E
self.memory[0x2] = 0x79
self.memory[0x3] = 0xE0
self.memory[0x4] = 0x4F
self.memory[0x5] = 0x1E
self.memory[0x6] = 0x2D
self.memory[0x7] = 0x4E
self.memory[0x8] = 0x60
self.memory[0x9] = 0x50
self.memory[0xA] = 0x4F
self.memory[0xB] = 0x1D
self.memory[0xC] = 0x4E
self.memory[0xD] = 1
self.memory[0xE] = 1
self.memory[0xF] = 0

I hope you understand it.

Running th code

Installation of Python 3.x version is required. Clone this repo git clone https://github.com/jaychandra6/EaterEmulator and run python3 cpu.py on Linux. If you are on Windows make sure that Python is added to your PATH and run python cpu.py.