— 4 —
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
