Locator/Intercom Mode; Telephone Line Interface - Panasonic KX-TG2240BXS Service Manual

KX-TG2240BXS / KX-TGA228BXS

16.5. Locator/Intercom Mode

1. When the base unit LOCATOR/INTERCOM button is pressed, a call monitor signal (intercom sound) is output from DSP (SPP,
SPN). Thus a monitor tone is heard from the speaker.
2. At the same time, flashing of the IN USE/CHARGE (LED900) is obtained from DSP (INUSE-LED). This status is called
"Intercom stand-by".
3. The receiving signal flows:
RF → DSP (SPP, SPN) → SP
4. The transmission signal flows:
MIC → C235, C236 → R213, R214 → DSP (MIN, MIP) → RF

16.6. Telephone Line Interface

Telephone Line Interface Circuit:
Function
• • • • Bell signal detection
• • • • ON/OFF hook and pulse dial circuit
• • • • Side tone circuit
• • • • Auto-disconnect circuit/Parallel connection detection circuit
Bell signal detection and OFF HOOK circuit:
In the idle mode, Q4 is open to cut the DC loop current and decrease the ring load. When ring voltage appears at the Tip (T)
and Ring (R) leads (When the telephone rings), the AC ring voltage is transferred as follows:
T, R → L1, L2 → R30, R31 → C16, C17 → Q6 → DSP (BELL) [BELL]
When the CPU (DSP) detects a ring signal, Q4 turns on, thus providing an off-hook condition (active DC current flow through
the circuit) and the following signal flow is for the DC line current.
T → D4 → Q4 → Q1 → R5 → D1 → D4 → L2 → POS1 → R [OFF HOOK]
ON HOOK Circuit:
Q4 is open, Q4 is connected as to cut the DC loop current and to cut the voice signal. The unit is consequently in an on-hook
condition.
Pulse Dial Circuit:
DSP (RYL) turns Q4 ON/OFF to make the pulse dialing.
Side Tone Circuit:
Basically this circuit prevents the TX signal from feeding back to RX signal.
As for this unit, TX signal feed back from Q1 is canceled by the echo canceller of DSP.
Note: DSP is IC201.
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