KX-TDA100DUP - Panasonic PBX Service Manual (repair manual). Page 126

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This transmits the DTMF signal on the highway timeslot. The different DTMF signals can be transmitted to the optional ports at
the same time.
They are transmitted to the line through CODEC.

During on-hook, transmitting the bell signal to the AC loop in the CR series circuits (C2 and R2) detects the current by Photo
Coupler (PC1,2), and it determines the presence of a bell signal. Software performs the operation for recognition and determina-
tion of a pattern of bell signals.
Bell loop path

• Ring

→L1→R2→PC2(1-2)→C3→R5→L1→TH1→Tip

In this path, PC1 4-pin converts from High to Low, and a bell signal is detected.

• Tip

→TH1→L1→R5→C3→PC2(1-2)→R2→L1→Ring

In this path, PC2 4-pin converts from High to Low, and a bell signal is detected.