Hudson Soft HuC6280


The HuC6280 8-bit microprocessor is Japanese company Hudson Soft's improved version of the WDC 65C02 CPU, an upgraded CMOS version of the popular NMOS-based MOS Technology 6502 8-bit CPU manufactured for Hudson by Seiko Epson and NEC for the SuperGrafx. The most notable product using the HuC6280 is NEC's TurboGrafx-16 video game console.

Description

The HuC6280 contains a 65C02 core which has several additional instructions and a few internal peripheral functions such as an interrupt controller, a memory management unit, a timer, an 8-bit parallel I/O port, and a programmable sound generator. The processor operates at two speeds, 1.79 MHz and 7.16 MHz.

Memory mapping

The HuC6280 has a 64 KB logical address space and a 2 MB physical address space. To access this entire memory space, the HuC6280 uses an MMU that splits the memory space into segments of 8 KB. The logical address space is split as follows:
RegisterPageLogical CPU address
MPR00$0000-$1FFF
MPR11$2000-$3FFF
MPR22$4000-$5FFF
MPR33$6000-$7FFF
MPR44$8000-$9FFF
MPR55$A000-$BFFF
MPR66$C000-$DFFF
MPR77$E000-$FFFF

Each logical 8 KB segment is associated with one of 256 physical 8 KB sized segment. This can be setup with an 8-bit register that contains the pointer of the 8 KB segment in physical memory to be mapped in this page. Two special instructions are used to access these registers:
TAMi, transfer the content of the accumulator into an MPR register.
TMAi, transfer an MPR register into the accumulator.

Sound generator

PSG-styled Wavetable Synthesis, provides 6 sound channels, which can be conveniently paired according to the functionality they provide:
0-1 - Waveform playback
Frequency modulation
2-3 - Waveform playback only
4-5 - Waveform playback
White noise generation
Waveform playback is the most common and allows a 32 byte, 5 bit unsigned linear sample to be played back at selected frequencies. Frequency modulation takes this one step further, allowing the playback frequency to be dynamically adjusted according to a specified pattern. White noise is used to simulate percussion instruments and effects, such as explosions, by means of a pseudo-random square wave.
Alternatively, each channel can be individually switched to "Direct D/A" mode in which the programmer can send data directly to the sound mixer, allowing more complex sound patterns to be generated, such as speech. Inevitably, this requires more programming effort and CPU time.