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docs/chibi_pc-09_technical_specification.md

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+# CHIBI PC-09 Technical Specification
+
+5-17-21 Amber Zeller
+
+## Quick Specs
+
+#### CPU
+
+1, 1.5, 2 MHz Motorola 6809
+
+#### Memory
+
+64k SRAM on external card for optional MMU capability. Seperated into 2k blocks, numbered 0-31. Only 62k of memory is accessible, due to the I/O block.
+
+#### I/O
+
+2k block, position 30. Addresses EFFF-F7FE. Further subdivided into 128 devices of 16 addresses each. 
+
+## Address Space Diagram
+
+| Address Range | Description            |
+| ------------- | ---------------------- |
+| 0000 - 07FF   | First Kernel Block     |
+| 0800 - EFFE   | Standard Memory Blocks |
+| EFFF - F7FE   | I/O Block              |
+| F7FF - FFFF   | Reset Vectors          |
+
+## I/O Block Description
+
+11 bits per block
+
+128 devices are possible, though will likely never be used. 
+
+| Bits | Description       |
+| ---- | ----------------- |
+| 0-6  | Device selection  |
+| 7-10 | Address selection |
+
+## Expansion Card Description
+
+Byte 0 of every card should contain a 'type' descriptor.
+
+| Type Descriptor | Description                     | Example |
+| --------------- | ------------------------------- | ------- |
+| 00              | Block Storage                   | SD Card |
+| 01              | ANSI I/O Stream                 | UART    |
+| 02              | ANSI Compatible Graphics Device | VGA64   |