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Famous pc historian and reverse engineer Ken Shirriff has turned his attentions to the Yamaha DX7 digital synth from the Nineteen Eighties — reverse engineering the operation of its TM21280 OPS operator chip from high-resolution die imagery.
“The Yamaha DX7 digital synthesizer was launched in 1983 and have become ‘one of the crucial essential advances within the historical past of recent standard music,'” Shirriff writes. “It outlined the sound of Nineteen Eighties pop music, utilized by bands from A-ha and Michael Jackson to Dolly Parton and Whitney Houston. The DX7’s electrical piano sound may be heard in over 40% of 1986’s prime hits.”
Ken Shirriff has labored tirelessly to seize a high-resolution die shot of Yanmaha’s TM21280 OPS, prepared for reversing. (📷: Ken Shirriff)
To dive deeper into precisely how the gadget labored, Shirriff eliminated the steel cowl from a TM21280 OPS chip — the so-called “operator” chip, one among two key customized chips within the synth alongside the YM21290 EGS “envelope” chip — and took over 100 photographs of the silicon by means of a microscope. By compositing these, Shirriff created a high-resolution picture of the circuitry — providing clues at how the 64-pin quad in-line package deal (QIP) did what it did.
“The shift registers are the most important blocks of the chip, particularly the part shift registers within the higher left,” Shirriff explains of his discoveries. “ROMs are the second-largest blocks, particularly the sine ROM and the 2 similar exponential ROMs. Adders present many of the logic circuitry; there is not a lot ‘random’ logic in comparison with a processor chip, for example. The chip has a number of bit shifters that shift a numeric worth, multiplying or dividing it by an influence of two.”
The chip drove Yamaha’s DX7, one of the crucial standard synth keyboards of the Nineteen Eighties. (📷: rockheim)
“Finding out the chip’s die reveals some attention-grabbing circuits. Uncovering the secrets and techniques of how the chip operates could assist construct extra correct DX7 emulators. The chip is complicated and this text simply scratches the floor so I plan to review the chip in additional element. Particularly, I intend to extract the information from the ROMs to search out out precisely how the waveforms are represented.”
Shirriff’s full write-up, which matches into the DX7’s operation and appears on the shift registers, ROMs, adders, bit shifters, and underlying algorithm in appreciable element, is now accessible on his web site.
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