## Sketching out our address space

### Memory Map

CPU Addressable

| Address | Usage                            |
| ------- | -------------------------------- |
| `$0000` | 32k ram (16k addressable)        |
| `$1000` | ...                              |
| `$2000` | ...                              |
| `$3000` | ...                              |
| `$4000` | I/0 & Hardware Control Registers |
| `$5000` | ...                              |
| `$6000` | 32k vram                         |
| `$7000` | ...                              |
| `$8000` | ...                              |
| `$9000` | ...                              |
| `$A000` | ...                              |
| `$B000` | ...                              |
| `$C000` | ...                              |
| `$D000` | ...                              |
| `$E000` | 32k eeprom (8k addressable)      |
| `$F000` | ...                              |

### Hardware Control Register $4000

| Bit       | 7            | 6            | 5        | 4             | 3                          | 2      | 1      | 0      |
| --------- | ------------ | ------------ | -------- | ------------- | -------------------------- | ------ | ------ | ------ |
| **Usage** | ROM Page MSB | ROM Page LSB | RAM Page | 32k Bank Page | Character/Hires Video Mode | Unused | Unused | Unused |

### Video Controls $4200 & $4201

When the system starts or when the video mode is changed, crt timing/character size information has to be sent to the 6845. This is done by writing

### Keyboard Rows $4300, $4301, $4302, $4303, $4304, $4305

Each keyboard row is mapped to a read-only 8-bit register, with each key mapped to a single bit. Due to the design of this keyboard, Row 5 has 5 unused bits

| Address | Desc  | Bit 7     | Bit 6  | Bit 5  | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0       |
| ------- | ----- | --------- | ------ | ------ | ----- | ----- | ----- | ----- | ----------- |
| `$4300` | Row 0 | `esc`     | `w`    | `e`    | `r`   | `t`   | `u`   | `o`   | `backspace` |
| `$4301` | Row 1 | `tab`     | `q`    | `s`    | `g`   | `y`   | `i`   | `p`   | `enter`     |
| `$4302` | Row 2 | `shift`   | `d`    | `v`    | `h`   | `k`   | `"`   | `?`   | `a`         |
| `$4303` | Row 3 | `control` | `z`    | `f`    | `b`   | `j`   | `l`   | `2`   | `4`         |
| `$4304` | Row 4 | `alt`     | `x`    | `c`    | `n`   | `m`   | `'`   | `1`   | `3`         |
| `$4305` | Row 5 | `meta`    | `sp 1` | `sp 2` |       |

### Character ROM Layout