Ricoh 5A22

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.

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

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. [cite web |url=http://www.romhacking.net/docs/memmap.txt |title=Anomie's SNES Memory Mapping Doc |accessdate=2006-04-13 |author=anomie |format=text ] It works at approximately 1.5 MIPS and has a theoretical peak of 1.79 million 16-bit adds per second.

References