50 lines
2.4 KiB
Markdown
50 lines
2.4 KiB
Markdown
## Sketching out our address space
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### Memory Map
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CPU Addressable
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| Address | Usage |
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| ------- | -------------------------------- |
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| `$0000` | 32k ram (16k addressable) |
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| `$1000` | ... |
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| `$2000` | ... |
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| `$3000` | ... |
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| `$4000` | I/0 & Hardware Control Registers |
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| `$5000` | ... |
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| `$6000` | 32k vram |
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| `$7000` | ... |
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| `$8000` | ... |
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| `$9000` | ... |
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| `$A000` | ... |
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| `$B000` | ... |
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| `$C000` | ... |
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| `$D000` | ... |
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| `$E000` | 32k eeprom (8k addressable) |
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| `$F000` | ... |
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### Hardware Control Register $4000
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| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
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| --------- | ------------ | ------------ | -------- | ------------- | -------------------------- | ------ | ------ | ------ |
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| **Usage** | ROM Page MSB | ROM Page LSB | RAM Page | 32k Bank Page | Character/Hires Video Mode | Unused | Unused | Unused |
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### Video Controls $4200 & $4201
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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
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### Keyboard Rows $4300, $4301, $4302, $4303, $4304, $4305
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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
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| Address | Desc | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
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| ------- | ----- | --------- | ------ | ------ | ----- | ----- | ----- | ----- | ----------- |
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| `$4300` | Row 0 | `esc` | `w` | `e` | `r` | `t` | `u` | `o` | `backspace` |
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| `$4301` | Row 1 | `tab` | `q` | `s` | `g` | `y` | `i` | `p` | `enter` |
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| `$4302` | Row 2 | `shift` | `d` | `v` | `h` | `k` | `"` | `?` | `a` |
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| `$4303` | Row 3 | `control` | `z` | `f` | `b` | `j` | `l` | `2` | `4` |
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| `$4304` | Row 4 | `alt` | `x` | `c` | `n` | `m` | `'` | `1` | `3` |
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| `$4305` | Row 5 | `meta` | `sp 1` | `sp 2` | |
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### Character ROM Layout
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