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Cardiograph Mark I — simulator for a paper computer

Dependencies

Node.js
- readline-sync

Run

Assemble

Hex output:
./run-assembler run source_code.asm

Binary output:
./run-assembler runbin source_code.asm

Verbose debugging output (hex):
./run-assembler debug source_code.asm

Assemble and run

With animated display of screen memory:
./run-cpu run source_code.asm

With verbose debugging output:
./run-cpu debug source_code.asm

With single stepping + pretty-printed display:
./run-cpu step source_code.asm

With single stepping + verbose debugging output:
./run-cpu stepdebug source_code.asm

Instruction set

00   END
01   STO lit#   ; store ... mem[lit#] <- A
02   STO addr   ; store ... mem[mem[addr]] <- A
03   LDA lit#   ; load  ... A <- lit#
04   LDA addr   ; load  ... A <- mem[addr]
05   ADD lit#   ; add   ... A <- A + lit#      ... and un/set carry flag
06   ADD addr   ; add   ... A <- A + mem[addr] ... and un/set carry flag
07   SUB lit#   ; sub   ... A <- A - lit#      ... and un/set carry flag
08   SUB addr   ; sub   ... A <- A - mem[addr] ... and un/set carry flag
09   HOP lit#   ; hop   ... skip next instruction if A == lit# ... when true: IP <- PC + 4
0A   HOP addr   ; hop   ... skip next instruction if A == addr ... when true: IP <- PC + 4
0B   JMP lit#   ; jump  ... IP <- lit#
0C   JMP addr   ; jump  ... IP <- addr
0D   FTG lit#   ; toggle flag by number (see details below)
0E   FHP lit#   ; flag hop ... skip next instruction if flag is set ... when true: IP <- PC + 4
0F   NOP ————   ; no operation

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

Registers and Flags

A - accumulator
IP - instruction pointer (aka program counter)
FLAGS - flags: Negative, Zero, Overflow, Carry
- in machine language, each flag is given a number:
  - N = 3
    Z = 2
    O = 1
    C = 0
- (bitwise, 0000 = NZOC)

Memory map / Peripherals

00-0F - display (4x4)
10-19 - reserved for future use
20 - keypad - value of the most recent keypress
21 - pointer to display memory
22 - pointer to keypad memory
23-2F - reserved for future use / variable storage
30 - initial value for IP
30-FF - free

Keypad

The value of the latest keypress on a hex keypad is stored at $20. (The keypad can also be relocated by changing the value of the pointer-to-keypad at $22.)

The keypad uses the same layout as the COSMAC VIP (and CHIP-8):

The CPU simulator maps the following Qwerty keys onto those values:

1 2 3 4
Q W E R
A S D F
Z X C V

Assembly language

ADD $01         ; comments follow a `;`

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

END             ; END and NOP don't require operands
                ; (the assembler will fill in a default value of 0)

@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 operand
                ; the label will be replaced with
                ; the address of the label

#foo $FF        ; define a constant
                ; (must be defined before it is referenced)

ADD #foo        ; use a constant as an operand

LDA *ADDR       ; `*ADDR` is a magic value referencing the memory address
                ; that the current line will store at after assembly

Hexadecimal numbers are preceded by a $
Whitespace is ignored

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