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