# [DRAFT] Design for the _MicroCardiograph_ microprocessor trainer

The MicroCardiograph uses memory-mapped IO.

## Memory map

| Address  | Used for...                                   |
|----------|-----------------------------------------------|
| 00 to 19 | display (5x5)                                 |
| 1A       | pointer to display memory                     |
| 1B       | keypad: value of latest key pressed           |
| 1C       | reserved for future use (bank switching flag) |
| 1D       | initial IP                                    |
| 1D to FE | free                                          |
| FF       | * ROM (unwriteable) pointer to initial IP     |

\* Not implemented yet


## Peripherals

### Keypad

The value of the latest keypress on a hex keypad is stored at `$1B`.

The keypad uses the same layout as the COSMAC VIP (and CHIP-8). The CPU simulator maps those keys onto a Qwerty set:

`1` `2` `3` `C`   =   `1` `2` `3` `4`  
`4` `5` `6` `D`   =   `Q` `W` `E` `R`  
`7` `8` `9` `E`   =   `A` `S` `D` `F`  
`A` `0` `B` `F`   =   `Z` `X` `C` `V`  

The arrow keys are also mapped onto the hex keypad:

` ` `5` ` `   =   ` ` `↑` ` `  
`7` `8` `9`   =   `←` `↓` `→`

### Keypad as monitor input

TODO