Ricoh 5A22

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The Ricoh 5A22 is the microprocessor CPU produced by Ricoh for the Super Nintendo Entertainment System (SNES) video game console. The 5A22 is based around the 16-bit CMD/GTE 65c816, itself a version of the WDC 65C816 (used in the Apple IIGS personal computer).

All of the above mentioned processors are based on the MOS Technology 6502 family of processors.

[edit] Major features

In addition to the 65C816 CPU core, the 5A22 contains support hardware, including:

Controller port interface circuits, including both serial and parallel access to controller data
An 8-bit parallel I/O port, which was mostly unused in the SNES
Circuitry for generating NMI interrupts on V-blank
Circuitry for generating IRQ interrupts on calculated screen positions
A DMA unit, supporting two primary modes:
- General DMA, for block transfers at a rate of 2.68MB/s
- H-blank DMA, for transferring small data sets at the end of each scanline outside of the active display period
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

[edit] Performance

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.^[1] It works at approximately 1.5 MIPS and has a theoretical peak of 1.79 million 16-bit adds per second.