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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.
Filter Block
Since the sound signal from the CPU is a stepped waveform, the filter block is added to smooth the
waveform.
From CPU
To main volume
Pin No. Terminal In/ Out Function
1, 2 TEST1, TEST2 Not used. Connected to ground.
3 RESET In
Power ON reset terminal. When the power switch is
turned on, the terminal receives a low level signal and
the internal circuits of the LSI are initialized.
4 AVDD In +5 V sorce for the built-in DAC
5 OUT Out Sound waveform output
6 AGND In Ground (0 V) source for the built-in DAC
7 GND In Ground (0 V) source
8, 9 COSI, COSO In/Out 21.725 MHz clock pulse input/output
10 VDD In +5 V source
11 ~ 18 KI0 ~ KI7 In Input terminal from keys and switches
19, 20 KO11, KO10 Not used.
21 ~ 30 KO9 ~ KO0 Out Key and switch scan signal output
VDD
C273(H) C473(H)
3.3K
1K
2.2K
C333(H)
T4
T3
2SC1740SQ
1K
150K
1.5K
120K
1K
C822(H)
C823(H)
AG
AG
AG
AG AG
2SC1740SQ