DX7
1. Keyboard and Panel Switch Scanning
The 4 bits B0 B3 from the sub-CPU (6805S) are
input to the decoder (40H138).
he 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)
the sub-CPU B4 and BS lines are low.
2. Key ON/OFF and Touch Data
,Ihe time it takes for the transfer contact to connect with the make contact after separating tram the break contact is recorded by the sub-CPU timer. This value is the Touch data.
The key ON signal is generated when the transfer comact connects with the m J~ce contact, and the key OFF signal is generated when the transfer car.tact connects with the break contact.
3. ADC
Data entry
Pitch bend wheel
Modulation wheel
Foot controller
Breath controller
After-touch controller
Battery voltage
The 7 analog control voltages given above are fed to the ADC (M58990P-1). The analog input selected by the sub-CPU BO – B2 bits is converted to a digital value when the sub-CPU B7 line goes low. The ADC outputs a high level to the sub-CPU C3 line when the
'rat conversion is complete. The ABC sends the S-bit
– – – – digital value to the sub-CPU when the sub-CPU B6
line goes low.
4. Data Transmission from Sub-CPU to i?lain
CPU
4 – I. When a key event occurs the sub-CPU CO line
goes hips, changing the state ot the ready tlag
(R S F/F) causing the m~in CPU IRQ ~nd P l
lines to go low
4 – 2. The main CPU accepts one byteot d ra on lines
AO – A7 from the sub-CPU when the P ! line
goes low.
4 – 3. Once this byte is accepted. pin 9 oi IC 4 goes
low, changing the state ot F/F and lorcir,g the
sub-CPU C 1 line low.
4 – 4. IVhen the sub-CPU Cl line oes low, ~-ep -l – i
(above) is repeated and then in step
second byte of data is accepted by the inain
8. LED
The LED display is created via software. The LEd are lit by data latched from the main CPU.
9. LCD
Data from the main CPU is decoded and display< at the LCD unit.
10. EGS (Envelope Generator)
8 bits of data are received from the main CPU, am envelope and frequency data are sent to OPS.
ll. OPS (Operator)
The OPS uses a sine table to generate vaveforr
data to be sent to the DAC from the received enve
ope and frequency data. The OPS perm
The OPS permits combining the 6 operators in 3
different combinations. Tlute combinations a.e cKei
"algorithms". One of the 6 operatcrs o able to tee<
the sine table output back to the input. The ieecbacJ
level and algorithm data is received from the mao
CPU.
12. DAC
A BA9221 DAC is used. The DAC converts the digital waveform data from the OPS to an actual analog waveform. The amplitude scale factor of the analog waveform is controlled via SFO – SF3. This signal is then fed to the sample 8c hold and low-pass filter circuits from which it is sent to the output terminal. A reference voltage is applied to pin 14 of the DAC. 8 reference voltages are ger.crated by the pPD4051, and the total level is externally controlled.
13. MIDI (Musical Instrument Digital lnteriace}
Permits data transfer with other devices. Data is received by F23 of the main CPU via a photo-coupler, and data is output from main CPU pili P24.