PC Engine CPU
A deep-dive into the HuC6280, the 8-bit CPU inside the TurboGrafx-16, revealing why a turbocharged 6502 at 7.16 MHz often outpaced the SNES despite the “16” in its name.
What Matters
- HuC6280 is a 65C02 derivative with 8-bit registers, 8-bit ALU, 8-bit data bus—nothing 16-bit despite the TurboGrafx-16 branding.
- Dual clock speeds: 1.79 MHz (NES parity) and 7.16 MHz; games almost universally issue CSH immediately at boot and stay there.
- 7.16 MHz with no memory latency penalty makes it typically more than 2× faster than the SNES CPU in practice, not just on paper.
- Built-in MMU maps 16-bit logical addresses to 21-bit physical (2 MB), using eight 8 KB MPRs—no cartridge mapper needed for most games.
- Five block-transfer instructions (TAI, TDD, TIA, TII, TIN) copy at 1 byte/6 cycles; they substitute for absent DMA hardware but block interrupts mid-transfer.
- Street Fighter II required a custom bank-switching mapper to handle its 2.5 MB ROM—the only PCE game with cartridge-side mapper hardware.
- [HN: @ndiddy] Hudson’s fast 8-bit approach beats Nintendo’s slow 16-bit choice when screen width is 256px and most calculations are 8-bit anyway.
- [HN: @nicole_express] The Arcade Card add-on was designed specifically around the block-transfer instructions; the SNES S-CPU also has an 8-bit data bus, weakening the 16-bit comparison.
