CASIO CTK401
Service Manual

CPU (LSI1: MSM6755B-17)
The CPU reads sound data from the ROM in accordance with the pressed key and the selected tone; the CPU can read rhythm data simultaneously when a rhythm pattern is selected. Then it provides the left and the right channels� waveforms separately, by converting the data into the waveforms with two built-in DACs. The CPU also controls key and button input. The following table shows the pin functions of LSI1.
Pin No. 1 2, 3 4 ~ 19 13 17 20 ~ 27 28, 29 30 31 32, 33 34 35 36 37 38 39 40 41 42, 43 44 45 46 47 48 49 50 51 52 53 54 55, 56 57 58 ~ 64 65 66 ~ 73 Terminal MA14 NCO MA0 ~ MA13 MRDB MCSB MD0 ~ MD7 NC1, NC2 DGND DVCC XTLO, XTLI NC3 RSTB P24/RXD P25/TXD NMI APO NC4 REFH NC5, NC6 DAOR NC7 AVdac DAOL REFL AGdac AGadc ANI AVadc NC8 MOD0 MOD1, MOD2 P40 KI0/P30 ~ KI7/P36 KI7/P37 KO0/P50 ~ KO7/P57 In/Out Out � Out Out � In/Out � In In In/Out � In � � In Out � Out � Out � In Out Out In In In In � In In � In � Out Function Address bus Not used Address bus Read enable signal Not used Data bus Not used Ground (0 V) source +5 V source 20 MHz clock input/output Not used Reset signal input Not used. Connected to +5 V. Not used Power ON signal input. Connected to +5 V. APO (Auto Power Off) signal output Not used Terminal for the internal DAC Not used Right channel sound waveform output Not used +5 V source for the internal DAC Left channel sound waveform output Terminal for the internal DAC and ADC Ground source for internal DAC Ground source for internal ADC APO cancellation signal +5 V source for the internal ADC Not used Mode selection terminal. Connected to +5 V. Mode selection terminal. Connected to ground. Not used Terminals for key/button input signal Not used Terminals for key scan signal
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