4.2.4Line current detection circuit
NA/TW models
NCU board
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| R87 |
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| 1 | 8 |
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| PC3 |
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| 2 | 7 |
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| C7 |
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| 3 | 6 |
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| PC3 |
| CN10 | 4 | Lb | R86 | 4 | 5 |
Line |
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19
CN9
20
SG
FAX board
| 19 | REVA1 | 66 |
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CN262 |
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| CN5 |
| 20 | REVB1 | 33 |
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MAIN board | ||
66 | 160 | |
CN5 | IC23 | |
ASIC | ||
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33 | 161 |
Fig.
The line current detection circuit consists of the photocoupler (PC3), ASIC (IC23) on the MAIN board and the other peripheral devices. It detects a dial tone and the hook status of the external telephone from the current flowing through the line.
When a dial tone is input from the telephone line, current flows through the line and the photocoupler is repeatedly turned ON/OFF. This allows the REVA1 and REVB1 to be the pulse signals and input to the ASIC, then the dial tone is detected.
When the handset is lifted from the external telephone, current also flows through the line and the pho- tocoupler is turned ON/OFF, then the
Signal Name | Type | Active |
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REVA1 | I | - | Line 1 | Current Detection Signal | IC23 |
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REVB1 | I | - | Line 1 | Reverse Current Detection Signal | IC23 |
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ELECTRICAL CIRCUITS |
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