YM2610
The YM2610 is a sound synthesis and playback chip made by Yamaha, which is used in all versions of the NeoGeo hardware. It was later merged with other chips in NEO-YSA and NEO-YSA2, which are used on some versions of the NeoGeo CD, the CDZ, the MV1C and on ROM-Only boards.
The YM2610 relies on a YM3016 external DAC (Digital to Analog Converter) chip for the FM and ADPCM sounds. The only direct analog output is for the SSG sounds. Both analog outputs are then mixed together before amplification.
The original YM2610 chip gets quite warm during normal operation.
Sound generation parts
Sound can come from 3 different generators, each having their own channels:
- SSG (Software Sound Generator): 4 channels
- FM (Frequency Modulation): 4 channels
- ADPCM (Sample playback): 7 channels
Programming
See Z80/YM2610 interface and YM2610 registers.
Multiplexed PCM bus
Access to the V ROMs are made via partly multiplexed buses. See YM2610 bus timing for more details about the access sequences.
The SDRMPX and SDPMPX signals are used to drive latches or the PCM chip in cartridges to demultiplex data. When SDROE or SDPOE goes low, SDRAD* and SDPAD* are tristated so that the V ROMs can output data.
- SDRA* for ADPCM-A
| SDRMPX | SDRAD* | SDRA* | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 20 | 21 | 22 | 23 | |
| Low to high | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | ? | ? | ? | ? |
| High to low | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 |
- SDPA* for ADPCM-B
| SDPMPX | SDPAD* | SDPA* | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | |||
| Low to high | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | ||
| High to low | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | ||
24 bits allow for 16MiB max V ROMs (without bankswitching).
Trivia
- A lot of games have several recordings of the same instrument playing different notes, rather than having only one sample and change the ADPCM-B playback frequency to vary its pitch. (Trumpet in Viewpoint, electric guitar in Super Sidekicks). Why ?
- Nazca's sound drivers are able to use the SSG channels for music playback. (Maybe all can ?)
Datasheet
Japanese datasheet: [ajworld.net] Incomplete/translated datasheet: [YM2610.pdf]