Yamaha Dx7 Service Manual

DX7 CIRCUIT DESCRIPTION
1. Keyboard and Panel Switch Scanning
The 4 bits BO ~ B3 from the sub-CPU (6805S) are input to the decoder (40H138).
The decoder output is sent to the keyboard transfer contacts and the panel switches.
The on or off state of the keyboard break contacts, make contacts and panel switches are sent to
the sub-CPU AO  ~ A7 lines via a line driver (40H240) when the sub-CPU B4 and B5 lines are
low.
2. Key ON/OFF and Touch Data
The time it takes for the transfer contact to connect with...

4-6. Data is not accepted from the panel switches and keys while the sub-CPU C2 line is
low.
5. Main CPU Operation
The main CPU mode is set by externally initializing lines P20~P22. When “L, L, H” is applied to
the P20~P22 lines and latched into the CPU on the rising edge of RES, the Extended Multiplex
Mode is selected.
In this mode, P40 ~ P47 function as address lines. The lower address bits are multiplexed with the
data on lines P30 ~ P37, and are separated by the address strobe signal SCI.
P20 ~ P24...

9. LCD
Data from the main CPU is decoded and displayed at the LCD unit.
10. EGS (Envelope Generator)
8 bits of data are received from the main CPU, and envelope and frequency data are
sent to OPS.
11. OPS (Operator)
The OPS uses a sine table to generate waveform data to be sent to the DAC from the
received envelope and frequency data.
The OPS permits combining the 6 operators in 32 different combinations. The combina-
tions are called “algorithms”. One of the 6 operators is able to feed the sine table...