Yamaha YM2612
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Yamaha YM2612
The YM2612, aka OPN2, is a six-channel sound chip developed by Yamaha. It belongs to Yamaha's OPN family of FM synthesis chips ud in veral game and computer systems. Developed as a stripped-down version of the YM2608, it lacks its larger sibling's ADPCM channel, Rhythm Sound System, SSG components, and GPIO ports. It also includes a sim
plified sound mixer with integrated DAC. It was also available in CMOS form, as the YM3438, aka OPN2C. It was most notably ud in the Sega Mega Drive/Sega Genesis game console and Fujitsu's FM Towns computer ries. As the YM3438, it was ud by Sega in various arcade game systems, including the Mega-Play, System 18, and System 32.
The YM2612 has the following features:
∙ Six concurrent FM channels (voices) 哪托福培训好
∙ Four operators per channel
∙ Two interval timers
∙ A sine-wave low frequency oscillator
∙ 斑秃原因Analogue stereo output (most other contemporary Yamaha FM chips require a parate external digital-to-analog converter chip)
∙ For channel three, operator frequencies can be t independently, making dissonant harmonics possible. (Normally, they would have a simple relation 2x or 3x relative to a common ba frequency.)
∙ Per-channel programmable stereo sound (Left, Right, or both Left and Right)
∙ Patch compatibility with Yamaha DX/TX synthesizers
The major difference between the YM2612 and the YM2608 is the removal of the original accumulator-equipped sound mixer, which mixed together the 14-bit floating point output of the FM channels. Instead it us a simpler time-division sound multiplexer, which first truncated the 14-bit channel output to 9-bits, then rapidly looped through outputting each channel. This truncating caud a "glitch" as the waveform approached the zero (neither positive or negative) point, known as the "ladder effect". External sound filtering circuitry was ud to reduce some of the noi generated by the truncating and channel looping, reducing the sound quality even more.
Along with the mixer changes, the chip was stripped of its predecessor's SSG component, although its vestigial SSG envelope generator is still functional.
The sixth channel can act as a surrogate PCM channel by means of the 'DAC Enable' register, allowing the chip to play 8-bit PCM sound samples. Enabling the register disables FM output for that channel. PCM data is written to the channel via an 8-bit register. The YM2612 does not provide any timing or buffering of the PCM samples, so all frequency control and buffering must be done in software by the host processor.
The YM3438, aka OPN2C, the CMOS form of the YM2612, changed the Channel 6 DAC output to the same 9-bit output in FM mode. The chip also had higher output impedance, requiring heavier external noi filtering circuitry but outputting louder sound. Sega ud an improved version of the OPN2C for the Model 2 version of the Mega Drive/Genesis, without the bit-depth truncating en in the original OPN2 and OPN2C.
[edit] Pinout
# | Pin | Function | 1/12 | GND | Ground Terminals | 2–9 | D0 – D7 | 8-bit Bidirectional data bus | 10 | NC | Not connected | 11 | /IC | System ret, initialize registers, active low | 13 | /IRQ | Maskable Interrupt Request, active low | 14 | /CS | Chip Select, active low | 15 | /WR | Write mode on data bus, active low | 16 | /RD | Read mode on data bus, active low | 17 | A0普雷斯利 | Read/Write Enable, active high | 18 | A1 | Part 1 / Part 2 lect (low=1, high=2) | 19 | A.GND | Analog Ground Terminal for internal D/A converter | 20–21 | MOL, MOR | Analog sound outputs, left and right | 22 | A.Vcc | Analog Vcc Terminal for internal D/A converter | 23 | Vcc | +5V Power Terminal | 24 | øM | Master Clock (7.67 MHz recommended) | | | |
| /CS | /RD | /WR | A0 | A1 | State of Data Bus | 英文绕口令 | 财务费用 0 | 国庆节 诗歌 1 | 0 | 0 | 0 | Selects Part 1 Register | 0 | 1 | 0 | 1 | 0 | Writes data to lected Part 1 Register. | 0 | 0 | 1 | 1 | 0 meet joe black | Reads the status of Part 1. | 0 | 1 | 0 | 0 | 竞争与合作 作文1 | Selects Part 2 register | 0 | 1 | 0 | 1 | 1 | Writes data to lected Part 2 register. | 0 | 0 | 1 | 1 | 1 | Reads the status of Part 2. | toyota什么梗 1 | × | × | × | × | D0 through D7 become high-impedance. | | | | | | |
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[edit] Example circuit
An example schematic for the YM2612 can be found here.
[edit] See also
∙ Yamaha YM2608
∙ Yamaha YM2203
∙ Sound chip
∙ VGM
∙ GYM
[edit] References
∙ Chipdir
∙ The infamous SEGA2.DOC
∙ spritesmind – New Documentation: An authoritative reference on the YM2612
∙ YM3438 info on x68000.de
∙ YM3438 Application Manual (Japane)
[hide] ∙ v · ∙ d · ∙ e Yamaha sound chips | | | PSG | YM2149F (SSG) | | | OPL | YM3526 (OPL) • YM2413 (OPLL) • Y8950 (MSX-Audio) • YM3812 (OPL2) • YMF262 (OPL3) • YMF278 (OPL4) | | | OPN | YM2203 (OPN) • YM2608 (OPNA) • YM2610 (OPNB) • YM2612 (OPN2) • YM3438 (OPN2C) • YMF288 (OPN3) | | | peeping OPS | YM21280 (OPS) • YM21290 (EGS) | | | Misc | YM2151 (OPM) • YM2164 (OPP) • YM3806 (OPQ) • YM3420 (OPU) • YMF271 (OPX) • YM2414 (OPZ) • YMF292 (SCSP) • YMF7xx (DS-1) | | | DAC | YM3012 (DAC-MS) • YM3014B (DAC-SS) • YM3016 (DAC-GS) • YAC513 | | |
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