(docs) readme - Add intro + re-arrange, to clarify relationship between Cardiograph and its constituent parts
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readme.md
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readme.md
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# Cardiograph Mark I — simulator for an imaginary computer
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## Dependencies
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Cardiograph is an imaginary computer. It has three main components:
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- Node.js
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1. the CPU, *Card* (short for 'Completely Analogue Risc Machine')
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2. an input-output processor, *IO*
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3. a display, *Graph*
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## Run
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## Simulator
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### Assembler
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### Run assembler
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```./assembler.js source_code.asm [output.txt]```
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By default, the output is written to `out.txt`. It is saved as a string of space-separated decimal numbers.
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### Simulator
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### Run simulator
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```./cardiograph.js < machine_code.txt```
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### Dependencies
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## Registers and Flags
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- Node.js
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## CPU
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### Registers and Flags
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- `A` - accumulator
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- `IP` - instruction pointer (aka program counter)
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@ -31,9 +39,9 @@ By default, the output is written to `out.txt`. It is saved as a string of space
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- (bitwise, `0000 = ONZC`)
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## Instruction set
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### Instruction set
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### Operations
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#### Operations
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```
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Hex Mnem. Operand Effect
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@ -60,7 +68,7 @@ Hex Mnem. Operand Effect
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one byte for the opcode, one for the operand
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### Effects on memory, flags, registers
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#### Effects on memory, flags, registers
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```
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op mem flags IP
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@ -87,50 +95,13 @@ FTG r ONZC +2
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FHP r ONZC +2/+4
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```
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## CPU start-up
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### Start-up
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When starting up, the CPU executes a `JMP $FF`.
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Put differently: it starts executing instructions at the address contained in `$FF`.
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## Cardiograph memory map
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- `00-19` - display (5x5)
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- `1A ` - pointer to display memory
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- `1B ` - keypad: value of latest key pressed
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- `1C ` - reserved for future use (bank switching flag)
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- `1D ` - initial IP
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- `1D-FE` - free
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- `FF ` - ROM (unwriteable) pointer to initial IP (not yet implemented)
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## Peripherals
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### Keypad
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The value of the latest keypress on a hex keypad is stored at `$1B`.
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The keypad uses the same layout as the COSMAC VIP (and CHIP-8). The CPU simulator maps those keys onto a Qwerty set:
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```
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1 2 3 C 1 2 3 4
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4 5 6 D Q W E R
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7 8 9 E A S D F
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A 0 B F Z X C V
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hex pad simulator
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```
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The arrow keys are also mapped onto the hex keypad:
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```
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5 ↑
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7 8 9 ← ↓ →
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hex pad simulator
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```
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## Assembly language
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### Assembly language
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ADD $01 ; comments follow a `;`
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@ -157,4 +128,40 @@ hex pad simulator
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; where the current line will be stored after assembly
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- Hexadecimal numbers are preceded by a `$`
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- Whitespace is ignored
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- Whitespace is ignored
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## Cardiograph memory map
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- `00-19` - display (5x5)
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- `1A ` - pointer to display memory
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- `1B ` - keypad: value of latest key pressed
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- `1C ` - reserved for future use (bank switching flag)
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- `1D ` - initial IP
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- `1D-FE` - free
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- `FF ` - ROM (unwriteable) pointer to initial IP (not yet implemented)
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## Cardiograph peripherals
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### Keypad
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The value of the latest keypress on a hex keypad is stored at `$1B`.
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The keypad uses the same layout as the COSMAC VIP (and CHIP-8). The CPU simulator maps those keys onto a Qwerty set:
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```
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1 2 3 C 1 2 3 4
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4 5 6 D Q W E R
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7 8 9 E A S D F
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A 0 B F Z X C V
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hex pad simulator
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```
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The arrow keys are also mapped onto the hex keypad:
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```
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5 ↑
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7 8 9 ← ↓ →
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hex pad simulator
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```
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