About

This software simulates the breadboard computer made by Ben Eater. You can write programs for it using Ben Eaters assembly language or directly write binary code. It was made by Luis Michaelis. You are allowed to edit this program and redistribute it as it is free and open source software.

Setup & Usage

For this program to run you will need Python 3.6 which you can download for all platforms from python.org.

To start open a terminal or command-line window in the folder of the program. Type in:

    python[3] cpu.py test.prg.bin

For linux users the command is python3 This will launch the included test program which counts up until it reaches 256, then it counts down until it reaches 0 and does this in a loop. To see the assembly code just open the test.prg in your favourite text editor. This code needs to be compiled before it can be used. To compile the code type in a terminal:

    python[3] compiler.py test.prg

This will compile the assembly code stored in test.prg into the compiled file test.prg.bin. You can open this file with a text editor too and see the compiled binary code.

To summarize: You can compile your program using:

    python[3] compile.py [yourfilename]

You can run the program by typing:

    python[3] cpu.py [youfilename].bin

Unless your program has a specific HLT instruction, the program will run forever.

To exit the program gracefully, send a KeyboardInterrupt (CTRL+C).

For more information about the programs type: python[3] [program].py -h

Writing Code

You can write your code either in Ben Eater's assembly language or directly write binary code. For convenience, here the table of assembly code, binary representation and description:

Assembly	Binary	Description	Argument
NOP	0000 xxxx	Do nothing (No Operation)	Not Required (set to 0)
LDA	0001 xxxx	Load value from RAM into the A register (Load A)	Required (memory location)
ADD	0010 xxxx	Add a value from RAM to the value in the A register and put the result back into the A register (Add)	Required (memory location)
SUB	0011 xxxx	Subtract a value from RAM from the value in the A register and put the result back into the A register (Subtract)	Required (memory location)
STA	0100 xxxx	Store the value in the A register into RAM (Store A)	Required (memory location)
LDI	0101 xxxx	Load a immediately using the argument (Load immediately)	Required (number to load)
JMP	0110 xxxx	Jump to a specified 'line' in code (!Lines start at 0) (Jump)	Required (line number)
JPC	0111 xxxx	Jump to a specified 'line' in code (!Lines start at 0) if the result of the previous operation was less than 0 or more than 255 (Jump Carry)	Required (line number)
JPZ	1000 xxxx	Jump to a specified 'line' in code (!Lines start at 0) if the result of the previous operation was equal to 0 (Jump if Zero)	Required (line number)
OUT	1110 xxxx	Write the value in the A register to the CLI (Output)	Not Required (set to 0)
HLT	1111 xxxx	Halt the system (Halt)	Not Required (set to 0)

Rules

• Line starts either with instruction or memory address and colon:

Assembly:

ADD 15
15: 5

Binary:

0010 1111
1111: 00000101

Line with memory address specifies variable address:variable Line without specifies instruction

• Except variables (255/0b11111111), all given numbers may not be larger than 15/0b1111

• Hashes (#) introduce comments

• PLEASE NOTE THAT MEMORY LOCATIONS WILL OVERWRITE IF THEY ARE SET MULTIPLE TIMES. This also applies for instructions: Every instruction gets automatically a space in memory, starting at 0000 and incrementing by one for every detected instruction:

Assembly

LDA 15  # Memory address 0
OUT 0   # Memory address 1 (and so on ...)

15: 6   # Memory address 15

Binary

0001 1111 # Memory address 0
1110 0000 # Memory address 1 (and so on ...)

1111: 00000110 # Memory address 15

The simulation program (cpu.py) can only run compiled binary code which could either be written by yourself or be result of the compiler. The compiler (compiler.py) only compiles assembly files.