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The Ricoh 5A22 is a microprocessor produced by Ricoh for the Super Nintendo Entertainment System (SNES) video game console. The 5A22 is based on the 16-bit CMD/GTE 65c816, itself a version of the WDC 65C816 (used in the Apple IIGS personal computer). It has a 16-bit accumulator, a 24-bit address bus, and is based on the MOS Technology 6502 family of processors.
In addition to the 65C816 CPU core, the 5A22 contains support hardware, including:
- Controller port interface circuits, including serial access to controller data
- An 8-bit parallel I/O port, which is mostly unused in the SNES
- Circuitry for generating non-maskable interrupts on V-blank
- Circuitry for generating interrupts on calculated screen positions
- A DMA unit, supporting two primary modes:
- Multiplication and division registers
- Two separate address busses driving the 8-bit data bus: a 24-bit "Bus A" for general access, and an 8-bit "Bus B" mainly for APU and PPU registers
The CPU as a whole employs a variable-speed system bus, with bus access times determined by the memory location accessed. The bus runs at 3.58 MHz for non-access cycles and when accessing Bus B and most internal registers, and either 2.68 or 3.58 MHz when accessing Bus A. It runs at 1.79 MHz only when accessing the controller port serial-access registers. It works at approximately 1.5 MIPS and has a theoretical peak of 1.79 million 16-bit adds per second.
- anomie. "Anomie's SNES Memory Mapping Doc" (text). Retrieved 2009-03-16.
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