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Paper computer simulator experiment

To do

Computer:

Implement carry flag on SUB

Misc:

Write some more complex test programs
- Display (hex) numbers
Do a proper binary version... (or lose the typed arrays?)
Extract debugging to its own module
Think about automated testing

Run the assembler/simulator

Assemble source code:
npm run assemble source_code.asm

Assemble and run, with animated display of screen memory:
npm run display source_code.asm

Assemble and run, with debug output:
npm run debug source_code.asm

Instruction set

0   END
1   STO lit#   ; store ... mem[lit#] <- A
2   STO addr   ; store ... mem[mem[addr]] <- A
3   LDA lit#   ; load  ... A <- lit#
4   LDA addr   ; load  ... A <- mem[addr]
5   ADD lit#   ; add   ... A <- A + lit#      ... and un/set carry flag
6   ADD addr   ; add   ... A <- A + mem[addr] ... and un/set carry flag
7   SUB lit#   ; sub   ... A <- A - lit#      ... and un/set carry flag
8   SUB addr   ; sub   ... A <- A - mem[addr] ... and un/set carry flag
9   HOP lit#   ; hop   ... skip next instruction if A == lit# ... when true: IP <- PC + 2
A   HOP addr   ; hop   ... skip next instruction if A == addr ... when true: IP <- PC + 2
B   JMP lit#   ; jump  ... IP <- lit#
C   JMP addr   ; jump  ... IP <- addr
D   CCF ————   ; clear Carry Flag ... CF = 0
E   CHP ————   ; carry hop ... skip next instruction if Carry Flag is set ... when true: IP <- PC + 2
F

Instructions are two bytes long: one byte for the opcode, one for the argument

Nice features that didn't fit

Hop IF< and hop IF>
MUL and DIV
Rotates and shifts

Registers and Flags

A - accumulator
IP - instruction pointer (aka program counter)
CF - carry flag

Memory map / Peripherals

00 - pointer to screen memory
01 - pointer to keypad memory
02-0F - reserved for future use
10-1F - display (4x4)
20-2F - keypad? (details TBD)
30 - initial value for IP
30-FF - free

Maybe someday

Timer (for a version in software/electronic-hardware)

Assembly language

ADD $01         ; comments follow a `;`

ADD $FF         ; this is direct addressing
ADD ($CC)       ; this is indirect addressing

END             ; END, CFC, and CHP don't require arguments
                ; (a default value of 0 will be used as their operand)

@subroutine     ; create a label
    ADD $01     ; (it must be on the line before the code it names)
    ADD $02

JMP @subroutine ; use a label as an argument
                ; the label will be replaced with
                ; the address of the label

Hexadecimal numbers are preceded by a $
Whitespace is ignored

2.8 KiB Raw Blame History