KX-NS0180X - Panasonic PBX Service Manual (repair manual). Page 11

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This is detected by the photo coupler (pin 4 of PC1 and PC2) at part of making DC loop. PC1(PC2) 4-pin is High level during a call.
However, at end-call, PC1(PC2) 4-pin converts from High to Low.
It detects an end-call with measuring of the signal width of Low level by CODEC (e.g. pin 39 of IC203, REVDET/ pin 38 of IC203,
BELLI).
The available setting values for detection width are none, 0.5msec-8msec(at 2msec intervals) and 16~896msec(at 8msec inter-
vals).

Configured by the photo couplers (PC1, PC2) that enable to detect each current in Tip

→Ring, Ring→Tip direction. (PC2 is used in

common as the bell detection photo coupler). Using Software, it stores the current direction (the detected photo coupler) at acquir-
ing line and recognizes the action by changing of the current direction (the detected photo coupler changes).

When the current flows in the direction of Ring to Tip, 4-pin of PC1 is Low and 4-pin of PC2 is High.

• Ring

→L1→R2→PC1 (1-2)→D3→RL3→Q4 (C-E)→R14→D3→L1→J2→L1→TH1→Tip

When the current direction (polarity) is reversed from Tip to Ring, 4-pin of PC1 turns to High and 4-pin of PC2 turns to Low. It recog-
nizes the action by changing of the current direction (the detected photo coupler changes).

• Tip

→TH1→L1→D3→R14→Q4 (C-E)→RL3→D3→PC2 (1-2)→R2→L1→Ring