Reverse engineering Yamaha DX7 synth chip

By ivke2006

Expert (78)

ivke2006's picture

16-11-2021, 15:54

Interesting blog about reverse engineering the dx7 synth chip.

Maybe someone should donate some MSX chips to Ken? :)

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By friguron

Master (177)

friguron's picture

17-11-2021, 02:05

OH MY GOAT... I wonder if/when DEXED project might improve its core emulation modules if its authors reach this material...

By Grauw

Ascended (10313)

Grauw's picture

26-11-2021, 15:31


The schematic below shows how one stage of the shift register is implemented. The chip uses a two-phase clock. In the first phase, clock ϕ1 goes high, turning on the first transistor. The input signal goes through the inverter, through the transistor, and the voltage is stored in the capacitor. In the second phase, clock ϕ2 goes high, turning on the second transistor. The value stored in the capacitor goes through the second inverter, through the second transistor, and to the output, where it enters the next shift register stage. Thus, in one clock cycle (ϕ1 and then ϕ2), the input bit is transferred to the output. (The circuit is similar to dynamic RAM in the sense that bits are stored in capacitors. The clock needs to cycle before the charge on the capacitor drains away and data is lost. The inverters amplify and regenerate the bit at each stage.)

This explains why there is a lower bound to the clock frequency that the Yamaha FM chips can operate on, as andete and wouterv found in their YM2413 reverse engineering project.