CPU (MSM6387-13)
The CPU contains a sound data ROM and a DAC (Digital to Analog Convertor), and it provides a sound
waveform in accordance with the pressed key and the selected tone.
The following table shows the pin functions of the CPU.
Pin No.TerminalIn/ OutFunction
1, 2TEST1, TEST2 Not used. Connected to ground.
Power ON reset terminal. When the power switch is
3RESETIn turned on, the terminal receives a low level signal and
the internal circuits of the LSI are initialized.
4AVDDIn +5 V sorce for the built-in DAC
5OUTOut Sound waveform output
6AGNDIn Ground (0 V) source for the built-in DAC
7GNDIn Ground (0 V) source
8, 9COSI, COSOIn/Out 21.725 MHz clock pulse input/output
10VDDIn +5 V source
11 ~ 18KI0 ~ KI7In Input terminal from keys and switches
19, 20KO11, KO10 Not used.
21 ~ 30KO9 ~ KO0Out Key and switch scan signal output
Filter Block
Since the sound signal from the CPU is a stepped waveform, the filter block is added to smooth the
waveform.
VDD
T3
120KC273(H) C473(H)
T4
2SC1740SQ
150K1.5K
3.3K1K2.2K
1K
From CPU
2SC1740SQ
AGAG
C333(H)
To main volume
1K
C822(H)C823(H)
AGAGAG
N 4 N |
ACEC
