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8

When the bell signal is input between T/R, the signal are outputted at the speaker via the following path:
T / R 

→ R1 / C1 → D1 / LED1(2AP) → IC1 (pin1) → IC1 (pin8) → PC1 → C5 → SW2 → T1 → Speaker

When [AOH] button is pressed during bell rings, self ringing circuit will be activated.
IC801 (pin 70) is changed from low to high logic, causing Q103, Q101 to turn on,  and resulting the set  is in off-hook status.
The bell signal from T/R stops and starts generating from IC801 via the following path:
IC801 (pin 57) 

→ Q2 → SW2-2 → IC601 (pin 19) → IC601 (pin 15) → Speaker.

In talk status, SW101 become ON and Q102 base changes to high level, causing Q102, Q103, Q101 to turn on and resulting in
a line loop. The loop current flows from D101(+) 

→ Q101 → Q107 → R119 → D103 in that order, A pulse signal that repeated

switches between high and low logic is output from pin 73 of the CPU. This switches the line loop on and off, generating the dial
pulse signal.

• On hook

Q101 is OFF, on-hook condition where DC loop is disconnected and voice signal flow is cut.

• Off hook

Q101 is ON*, providing an off-hook condition (active DC current flow through the circuit) and the following is the signal flow:
T 

→ POS101 → L101 → D101(+) → Q101 → Q107 → R119 → D103 → D101(-) → L102 → R

*  Handset mode : SW101 ON after handset off-hook
*  SP-Phone mode : IC801 (pin 70) output high logic after pressing SP-Phone button. 

• The receiving signal flows:

LINE 

→ Q101 → C109 → C401 → R401 → Q401 → Q402 → Q403 → SP (handset)

• The transmission signal flows

MIC (handset) 

→ Q422 → R433 → C432 → Q107 → Q101 → LINE

This circuit is used to sense the status of the line (busy tone or dial tone) during dummy ring generation and Auto Redial.

D101 

→ Q101 → C201 → R201 → R205 → Pin 5 of IC201 → Pin 1 of IC201 → D202 → R208 → Q201 → Pin 87 of IC801.

When the subscriber hangs-up, check the intermittent tone. If cycle tone is detected, the collector of Q201 goes to a low logic.

9

The circuit controls the automatic switching of the transmitted and received signals, to and from the telephone line, when the
unit is used in the hands -free mode.

The speakerphone can only provide a one-way communication path.
In other words, it can either transmit an outgoing signal or receive an incoming signal at a given time, but cannot do both simul-
taneously. Therefore, a switching circuit is necessary to control the flow of the outgoing and incoming signals.
This switching circuit is contained in IC601 and consists of a Voice Detector, TX Attenuator, RX Attenuator, Comparator and
Attenuator Control.  The circuit analyzes whether the TX(transmit) or the RX(receive) signal is louder, and then it processed the
signals such that the louder signal is given precedence.
The Voice Detector provides a DC input to the Attenuator Control corresponding to the TX signal.
The Comparator receives a TX and a RX signal, and supplies a DC input to the Attenuator Control corresponding to the RX sig-
nal.
The Attenuator Control provides a control signal to the TX and the RX attenuator to switch the appropriate signals on and off.
The Attenuator Control also detects the level of the volume control to automatically adjust for changing ambient conditions.

1. Transmission signal path:

The input signal from the microphone is sent through the circuit via the following path:MIC 

→ Pin 9 of IC601 → Pin 10 of

IC601 

→ Pin 3 of IC601 → Pin 4 of IC601 → R601 → C602 → Q107 → Tel line.

2. Reception signal path:

Signals receive from the telephone line are outputted at the speaker via the following path:Tel line 

→ Q107  → C401 → Q401

→ R600 → C603 → Pin 27 of IC601 → Pin 26 of IC601 → Pin 19 of IC601 → Pin 15 of IC601 → Speaker.

3. Transmission/Reception switching

The comparison result between TX and RX outputs as a DC level of Pin 25 of IC601.TX level is high ......  Pin 25 = Pin 21 -
6mV RX level is high ...... Pin 25 = Pin 21 - 150mVComparator output is connected to the attenuator control inside of IC601.

4. Voice detector

The output of the mic amp (Pin 10 of IC601) is supplied to Pin 13 of IC601 as a control signal for the voice detector.

5. Attenuator control

The attenuator control detects the setting of the volume control through Pin 24 of IC601 to automatically adjust for changing
ambient conditions.

This circuit is used to initialize the CPU when the batteries are installed.

10

When the batteries are inserted into the unit, then the voltage is regulated by IC302 and power is supplied to the CPU. The unit
starts operating soon after the voltage goes beyond point A in the voltage diagram. 

11

The caller ID is a chargeable ID which the user of a telephone circuit obtains by entering a contract with the telephone company
to utilize a caller ID service. For this reason, the operation of this circuit assumes that a caller ID service contract has been
entered for the circuit being used.
The Caller-ID data from exchange is supplied to the telephone using the method of FSK and displayed on LCD of the unit. 

• FSK (Frequency Shift Keying) format 

Caller ID
Caller ID signal is sent through the circuit via the following path:
LINE 

→ C501/C502 → C551/C552 → R551/R552 → R553/R554 → IC801 (pin 92, 93)