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# 16-bit CPU design doc
## Features
16-bit data
16-bit address width
16-bit instruction width
16-bit control word
Minimal instruction set computer (MISC)
4-bit opcodes
Memory mapped I/O
instruction format
xxxx xxxx xxxx xxxx - xxxx xxxx xxxx xxxx
General purpose registers:
RA (0) .. RH (7)
Expansion port that connects directly to the main bus
Default addressing mode: indirect absolute (addresses are stored in registers and point to a complete address). Some instructions use PC-relative addressing.
## Operations
TODO rewrite bit about operations
ALU flags:
- C = carry bit
- O = overflow bit
- Z = zero bit
- S = sign bit
Interrupt lines: ???
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