CPU (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 the CPU.
Pin No. | Terminal | In/ Out | Function | ||||
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1, 2 | TEST1, TEST2 |
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| Not used. Connected to ground. |
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| Power ON reset terminal. When the power switch is |
3 | RESET |
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| In | turned on, the terminal receives a low level signal and | ||
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| the internal circuits of the LSI are initialized. |
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4 | AVDD |
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| In | +5 V sorce for the | ||
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5 | OUT |
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| Out | Sound waveform output | ||
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6 | AGND |
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| In | Ground (0 V) source for the | ||
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7 | GND |
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| In | Ground (0 V) source | ||
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8, 9 | COSI, COSO | In/Out | 21.725 MHz clock pulse input/output | ||||
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10 | VDD |
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| In | +5 V source | ||
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11 ~ 18 | KI0 ~ KI7 |
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| In | Input terminal from keys and switches | ||
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19, 20 | KO11, KO10 |
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| Not used. |
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21 ~ 30 | KO9 ~ KO0 |
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| Out | Key and switch scan signal output | ||
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Filter Block
Since the sound signal from the CPU is a stepped waveform, the filter block is added to smooth the waveform.
To main volume
1K 2SC1740SQ
AG
T3
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| VDD |
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120K | C273(H) | C473(H) |
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150K | 1.5K | 2SC1740SQ | T4 |
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| 3.3K | 1K | 2.2K |
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| From CPU |
AG | C822(H) |
| C823(H) |
1K | C333(H) | ||
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AG | AG |
| AG |
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