Ricoh 5A22

Ricoh 5A22

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:
  • General DMA, for block transfers at a rate of 2.68 MB/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

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 performance of 1.79 million 16-bit operations per second.

• Super Nintendo Entertainment System technical specifications