25.5. CIRCUIT OPERATION
25.5.1. CO Interface Circuit
25.5.1.1. Composition
This is composed of the following circuit:
1) Bell signal detection
2) DC loop formation circuit
3) Pulse dial transmission circuit
4) CALL ID interface circuit
5) COL bidirectional amplifier circuit
1) Bell signal detection
When CO line is idle, photo coupler PC1, PC2 are OFF.
When there is an incoming signal from CO line, the current flows PC1 as in the following way.
Tip → L1 → R2 → PC1(1-2) → C3 → T2 → R5 → L1 → Ring: This cause pin4 of PC1 to change the level from High to low.
Ring → L1 → R5 → T2 → C3 → PC2(1-2) → R2 → L1 → Tip: This cause pin4 of PC2 to change the level from High to low.
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KX-TES824LA / KX-TEM824LA /
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