Casio casio electronic keyboard Nco, Mrdb, Mcsb, Dgnd, Dvcc, XTLO, Xtli, NC3, Rstb, P24/RXD, Nmi

CPU (LSI1: MSM6755C-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.	Terminal	In/Out	Function
1	MA14	Out	Address bus
2, 3	NCO	—	Not used
4 ~ 19	MA0 ~ MA13	Out	Address bus
13	MRDB	Out	Read enable signal
17	MCSB	—	Not used
20 ~ 27	MD0 ~ MD7	In/Out	Data bus
28, 29	NC1, NC2	—	Not used
30	DGND	In	Ground (0 V) source
31	DVCC	In	+5 V source
32, 33	XTLO, XTLI	In/Out	20 MHz clock input/output
34	NC3	—	Not used
35	RSTB	In	Reset signal input
36	P24/RXD	—	MIDI signal input
37	P25/TXD	—	MIDI signal output
38	NMI	In	Power ON signal input. Connected to +5 V.
39	APO	Out	APO (Auto Power Off) signal output
40	NC4	—	Not used
41	REFH	Out	Terminal for the internal DAC
42, 43	NC5, NC6	—	Not used
44	DAOR	Out	Sound waveform signal output
45	NC7	—	Not used
46	AVdac	In	+5 V source for the internal DAC
47	DAOL	Out	Left channel sound waveform output
48	REFL	Out	Terminal for the internal DAC and ADC
49	AGdac	In	Ground source for internal DAC
50	AGadc	In	Ground source for internal ADC
51	ANI	In	Not used
52	AVadc	In	+5 V source for the internal ADC
53	NC8	—	Not used
54	MOD0	In	Mode selection terminal. Connected to +5 V.
55, 56	MOD1, MOD2	In	Mode selection terminal. Connected to ground.
57	P40	—	Not used
58 ~ 64	KI0/P30 ~ KI7/P36	In	Terminals for key/button input signal
65	KI7/P37	—	Not used
66 ~ 73	KO0/P50 ~ KO7/P57	Out	Terminals for key scan signal

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