# Cardiograph-I — simulator for a paper computer

## Dependencies

Node.js

## 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```

## 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 + 2
    0A   HOP addr   ; hop   ... skip next instruction if A == addr ... when true: IP <- PC + 2
    0B   JMP lit#   ; jump  ... IP <- lit#
    0C   JMP addr   ; jump  ... IP <- addr
    0D   CCF ————   ; clear Carry Flag ... CF = 0
    0E   CHP ————   ; carry hop ... skip next instruction if Carry Flag is set ... when true: IP <- PC + 2
    0F   NOP ————   ; no operation

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


## Registers and Flags

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

## Memory map / Peripherals

- `00-0F` - display (4x4)
- `10-1F` - keypad? (details TBD)
- `20   ` - pointer to display memory
- `21   ` - pointer to keypad memory
- `22-2F` - reserved for future use / variable storage
- `30   ` - initial value for IP
- `30-FF` - free

## 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

    =foo $FF        ; define a constant
                    ; (must be defined before it is referenced)
    
    ADD =foo        ; use a constant as an operand

- Hexadecimal numbers are preceded by a `$`
- Whitespace is ignored