CASIO CTK50
Manual de Servicio

CPU (LSI201: 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 LSI201. Pin No. 1, 2 3 4 5 6 7 8 9 10 11 ~ 18 19, 20 21 ~ 30 Terminal TEST1, TEST2 RESET AVDD OUT AGND GND COSI COSO VDD KI0 ~ KI7 KO11, KO10 KO9 ~ KO0 Out In In In In Out In In In In/ Out Function Not used. Connected to ground. 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. +5 V sorce for the built-in DAC Sound waveform output Ground (0 V) source for the built-in DAC Ground (0 V) source 21.725 MHz clock pulse input Not used. +5 V source Input terminals from keys and switches Not used. Key and switch scan signal outputs
C202

FILTER BLOCK
Since the sound signal from the CPU is a stepped waveform, the filter block is added to smooth the waveform.
AVDD Q201 2SC1740SQ R203 R204

From CPU
C203

To main volume

R202
AG

C201

AG

�5�