SPC700

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Sony SPC700 Core microcontroller

The Sony SPC700 is an 8-bit sound chip that was designed by Ken Kutaragi and was used together with a digital signal processor (DSP) in the Super Nintendo Entertainment System (SNES) game console. The SPC700 and the associated 16-bit DSP were developed and manufactured by Sony . Sony later entered the game console market with the PlayStation . For that time (1990) the SPC700 chip was very advanced and can be limited even with today's wavetable - Synthesizer to compare sound cards.

technology

DSP developed by Sony

In the SNES, the SPC700 is mounted above the DSP. The sound chip contains 64 KB of RAM internally and runs at a clock frequency of 1,025.280 MHz (the audio clock runs at 24,606,720 Hz (necessary for the serial transmission of the samples to the DAC), which are divided into 3,075,840 Hz; by 3 The SPC700 receives the first cycle and the DSP receives the remaining 2 cycles). It has six internal registers and can execute 256 opcodes . SPC700 sound samples are stored in RAM in a compressed format comparable to ADPCM . The instruction set is similar to that of the 6502 CPU series, but contains additional instructions such as XCN (eXChange Nibble ), which swaps the upper and lower 4-bits of the output signal of the 8-bit register, and an instruction that contains an 8-bit x 8-bit multiplication and storage in a 16-bit register possible.

The DSP belonging to the SPC700 works similarly to modern wavetable sound cards, such as B. the Sound Blaster Audigy. Eight voices can be generated simultaneously in any suitable pitch and volume. It also supports voice panning , ADSR , echo with filtering (via a programmable 8-tap FIR ( Finite Impulse Response )), and the use of noise as a noise source (useful for certain sound effects such as wind). The output signal is generated as 16 bit stereo with a sampling rate of 32 kHz. The communication of the SPC700 with the DSP is done via memory mapped I / O .

SNES mainboard

The SPC700 has a rather unusual way of working for a sound chip. The main CPU of the SNES transfers blocks of data with commands and sound samples to the internal memory of the SPC700. These commands consist of machine code and were developed for the SPC700 in much the same way as for PCs or Macs . As such, the SPC700 can be seen as a coprocessor for the sound of the SNES. This is an advantage compared to the Game Boy Advance , where the ARM7 CPU has to do all the sound generation.

The emulation-related sound format "SPC" is derived from the name of this sound chip.

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