This is an assembler + simulator/emulator of Ben Eater's 8bit breadboard computer written in Python. The program is meant to be run on the command line, providing a text interface that uses unicode characters for drawing boxes and LEDs.

Use this program to:

• Write programs in assembly and run/debug them in the comfort of a laptop or desktop machine.
• Assemble a program into a binary listing that is ready to be programmed on the real machine using the DIP switches.
• Generate the microcode EEPROM binary contents ready to be written to an actual EEPROM chip.
• Make modifications to the microcode (for example, you can add more instructions) and see the result in the stimulator.
• Experiment with modifications to the simulated hardware before commiting to build it on the breadboards.

It has been tested on Windows and Linux, and is assumed to work just fine on other operating systems as long as they support the curses module in the Python standard library. The simulation is subcycle-accurate, meaning that the registers, control lines, RAM and 7-segment display are simulated during both the down-going and up-going flank of the clock. Making modifications to the code to match your specific breadboard build is meant to be easy. The code is short and to the point: there are only 4 short python files.

For a version with its RAM upgraded to 256 bytes following the instructions by /u/MironV, see, see the ext_memory branch of this repo.

Either clone the respository, or download the code. Run the simulator.py script using Python (version 3.5 or higher). On windows, you'll also need the windows-curses package to display the user interface (on other platforms, curses is included in the standard lib).

Write your test program in assembler and run it through the simulator:

python simulator.py example_programs/test.asm

Run your program without the interface, producing just the values sent to the 7-segment display:

python simulator.py --no-interface example_programs/test.asm

Assemble your program into a binary listing that you can program on the real machine using the DIP switches:

python assembler.py example_programs/test.asm

Write the microcode EEPROM contents to a binary file that you can use with EEPROM programmers:

python microcode.py binary_blob_for_EEPROM.bin

Load the microcode EEPROM contents from a binary file into the simulator, and run a test program:

python simulator.py --microcode binary_blob_for_EEPROM.bin example_programs/test.asm

Run the simulator.py, microcode.py and assembler.py scripts using the --help option to find out about even more functionality.

This simulator reads its memory contents from a text file with the .asm extension. The file should contain programming code written in assembler.

Supported assembler instructions:

nop     No operation
lda #   Load memory contents at # into register A
add #   Add memory contents at # to register A
sub #   Subtract memory contents at # from register A
sta #   Store contents of register A at memory location #
ldi #   Load the value # into register A
jmp #   Jump to memory location #
jc #    Jump to memory location # if the carry flag is set
jz #    Jump to memory location # if the zero flag is set
out     Output contents of register A
hlt     Halt the CPU, end of program

The assembler also supports comments using the ; character, writing raw values with db and labels. Here is an example assembler program that uses all the features of the assembler:

;
; Test program that adds two numbers
;
	lda a  ; Load the memory contents at the (a) label into register "A".
	add b  ; Add the memory contents at the (b) label to the value in register "A".
	out    ; Display the value in register "A" on the 7-segment display.
	hlt    ; Halt the clock. This signals the end of the program.

a:         ; Label that marks memory location (a)
	db 28  ; Write the literatal value "28" at this memory location.
b:         ; Label that marks memory location (b)
	db 14  ; Write the literal value "14" at this memory location.

More example programs can be found in the example_programs/ folder of this repository.