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The modem (IC5) has all the hardware satisfying the CCITT standards mentioned previously. 
When the ASIC IC1 (61) is brought to a low level, the modem (IC5) is chip-selected and the resistors inside IC are selected by the
select signals from ASIC (IC1) ADR0-ADR4. The commands are written through the data bus, and all the processing is controlled
by the ASIC (IC1) according to CCITT procedures. The INT signal dispatched from IRQ (pins 100 of IC5) to ASIC (IC1) when the
transmission data is accepted and the received data is demodulated, the ASIC (IC1) implements post processing. This modem
(IC5) has an automatic application equalizer. 
With training signal 1 or 2 during G3 reception, it can automatically establish the optimum equalizer. The modem (IC5) operates
using the 32.256 MHz clock (X3).

1. Facsimile Transmission

The digital image data on the data bus is modulated in the modem (IC5), and sent from pin 56 via Analog SW IC10, amplifier
IC9 and the NCU section to the telephone line.

Refer to Check Sheet for Signal Route (P.114).

2. Facsimile Reception 

The analog image data which is received from the telephone line passes through the NCU section and enters pin 47 of the
modem (IC5). The signals that enter pin 47 of the modem (IC5) are demodulated in the board to digital image signals, then
placed on the data bus.
In this case, the image signals from the telephone line are transmitted serially. Hence, they are placed on the bus in 8 bit
units. Here, the internal equalizer circuit reduces the image signals to a long-distance receiving level. 
This is designed to correct the characteristics of the frequency band centered about 3 kHz and maintain a constant receiving
sensitivity. It can be set in the service mode. 

Refer to Check Sheet for Signal Route (P.114).

3. DTMF Transmission (Monitor tone) 

The DTMF signal generated in the modem (IC5) is output from pin 56, and is then sent to the circuit on the same route as
used for facsimile transmission.

Refer to Check Sheet for Signal Route (P.114).

(DTMF Monitor Tone) 
Refer to Check Sheet for Signal Route (P.114).

4. Call Tone Transmission

This is the call signal which is generated in the ASIC (IC1) and sent to the speaker.

Refer to Check Sheet for Signal Route (P.114).

5. Busy/Dial Tone Detection 

The path is the same as FAX receiving. When it is detected, the carrier detect bit of the resistor in the modem (IC5) becomes
1, and this status is monitored by the ASIC (IC1).

6. Caller ID Detection 

The caller ID signal which is received from the telephone line enters pin 50 of the modem (IC5).

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It is composed of bell detection circuit, pulse dial circuit, line amplifier, sidetone circuits.

1. Circuit Operation 

The signal waveform for each point is indicated below. The signal (low level section) input to pin 19 of ASIC IC1 on the digital
board.
TEL LINE 

→ PC102 (1, 2 → 4) → CN101 (9) → {CN2 (9) →  IC1 (19)}

Note:{      } : inside the digital board

Normally (ON-HOOK condition), LINE RELAY (RLY101) is OFF. While OFF-HOOK, RLY101 turns ON. This LINE RELAY is con-
trolled by pin 130 of IC1 through the Q7.
ON-HOOK:
IC1 (130) Low Level 

→ Q7 OFF → RLY101 OFF

OFF-HOOK:
IC1 (130) High Level 

→ Q7 ON → RLY101 ON

Make state:
IC1 (130) High Level 

→ Q7 ON → RLY101 ON 

Break state:
IC1 (130) Low Level 

→ Q7 OFF → RLY101 OFF 

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1. Circuit Operation

The reception signal received as output from line transformer T101 is given as input to C108, R109 and IC101(2).
Then it is input to the reception system at an amplifier gain of 2.5 dB from pin (2).
The transmission signal is input from CN101 pin (6), and output to the TEL line through T101. Without a side tone circuit, the
transmission signal would return to the reception amplifier via C113 and R114. Here, the signal output from CN101 pin (6)
passes through C113, R113, R112, C109 and R110, and enters the amplifier IC101 pin (2). This is used to cancel the return
portion of the transmission signal. This is the side tone circuit.

1. Function

This circuit detects the signal (cuts the current) output from the converter when the other party finishes ICM recording and
goes into the ON-HOOK status.
TAD (Telephone Answering Device) detects this signal and disconnects the line. When the TAD is operating, pin (4) of PC102
becomes a low level.
While detecting the CPC signal, pin (4) of PC102 becomes a high level. When the CPC signal is detected, the TAD operation
stops and the line is disconnected.

1. Function

This circuit is used to detect that the telephone connected in parallel to the same line is OFF-hook while the unit picks up the
line. If this detection circuit is activated when TAM is being delivered, the delivery stops and the circuit is automatically
released.

2. Circuit Operation

If the line is picked up, C123 is charged by following the path shown below.
D109 (+) 

→ R136 → D107 → C123

When the electric potential difference between the base and emitter of Q104 becomes less than about 0.3V, Q104 and Q103
and PC101 turn off, then the IC1 pin 45 becomes a high level.
In this condition, if a telephone connected in parallel goes into OFF-hook status, the base of Q104 becomes low.
On the other hand, the emitter of Q104 goes down slowly because the capacitor (C123) is charged. Q104 turns on when the 
electric potential difference between the base and emitter of Q104 becomes more than 0.6 V while being charged. When
Q104 turns on, Q103 and PC101 also turn on, then the IC1 pin 45 becomes a low level.

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The unit receives the calling number from the central office.
RCID contains numbers only.
When a telephone line is captured after the bell rings, 500Hz of ACK signal is sent to the line and the dual tone signal is output.
The calling number is recognized by the digit number corresponding to the dual tone.

The outline of RCID TX/RX is shown below.

1. Receiving Signal

The Caller ID signal input from TEL LINE is processed with MODEM (IC5). Signal route is same as FAX receiving signal (FAX
RX). Refer to Check Sheet for Signal Route (P.114).

2. ACK signal

ACK signal is generated to the TEL LINE by ASIC (IC1). Signal route is as follows :

IC1(28) 

→ C55 → R42 → R46 → R49 → Q17(B-E) → C69 → IC10(4-3) → C77 → R57 → IC9(6-7) → CN2(6) → CN101(6)

→ C113 → R114 → T101 → TEL LINE