Casio ML-2 - CPU (LSI1: MSM6521-11); Filter Block

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CPU (LSI1: MSM6521-11)
Containing a sound data ROM and a DAC (Digital to Analog Converter), the CPU provides sound wave-
form in accordance with the pressed key and selected tone. The CPU also drives LEDs in the illuminated
keyboard directly. The following table shows the pin functions of LSI1.
Filter Block
Since the sound signal from the CPU is a stepped waveform, the filter block is added to smooth the
waveform.
Pin No. Terminal In/Out Function
1 ~ 7 LY1 ~ LY7 Out Keyboard LED drive signal output
8 LVDD1 In +5V source for the built-in LED driver
9 LGND2 In Ground (0V) source for the built-in LED driver
10 ~ 13 LX0 ~ LX3 Out Keyboard LED drive signal output
14 ~ 17 LX4 ~ LX7 Out Not used.
18 LVDD2 In +5V source for the built-in LED driver
19 GND2 In Ground (0V) source
20, 21 COSI, COSO In/Out 21.725 MHz clock pulse input/output
22 VDD In +5V source
23 GND1 In Ground (0V) source
24 ~ 26 TEST1 ~ TEST3 In Not used. Connected to ground.
27 RESET In Reset signal input. Power OFF: 0V, Power ON: +5V
28 AVDD In +5V source for the built-in DAC
29 OUT Out Sound waveform output
30 AGND In Ground (0V) source for the built-in DAC
31 ~ 38 KI0 ~ KI7 In Input terminal for keys and switches
39 ~ 46 KO0 ~ KO7 Out Key and switch scan signal input
47 ~ 58 Not used.
59 LGND1 In Ground (0V) source for the built-in LED driver
60 LY0 In Keyboard LED drive signal output
AVDD
AG
AG
AG
C11
C12
T2
2SC1740SQ
AG
C9
R1
R11
R30
C10
R12
R13
R14