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Circuit Description
5-7. LIU PBA
The LIU (Line Interface Unit) interfaces the MODEM and telephone to the telephone line. The FAX and
telephone portions of the LIU are active with machine power on. When machine power is off, only the
telephone circuity operates, powered by telephone line voltage. The FAX portion of LIU consists of the interface
between MODEM and telephone line, and the circuits for DC loop feeding, DP signal, loop current and ring
detect. The telephone portion is divided into ringer, dialling and speech circuits. Refer to the schematic and
connection diagram sections of this manual.
5-7-1. FAX section
MODEM/LINE INTERFACE
Following is the path for data and remote control
signals:
¥ CML1 relay: Switches telephone line between FAX
and telephone circuits.
¥ U1 pin 3TIT: Single ended input for transformer
(T2)
TIT: Transformer Input from Transformer
¥ U1 pin 40 ROT: Output for driving transformer
(T3) with an AC impedance greater than 10 Kohm.
ROT: Receive Output Transformer
¥ C57: DTMF and CNG detect path to T1 20Kohm
winding under idle conditions, and DC blocking
for 20Kohm winding.
¥ AC impedance: The AC impedance of U1 (I-LIU)
is set to 1000 ohm by external capacitor (C32) at
U1 pin 8 CI (Complex Impedance Input) port.
With the external resistor (R38) at U1 pin 34 ACI
port, it can be programmed to 600ohm. U1 pin 35
CS (Current Shunt control output) port is an
N-channel open drain output to control the
external high power shunt transistor for
synthesizing AC and DC impedance.
¥ DC conditions: The normal operating mode is
from 15mA to 100mA. An operating mode with
reduced performance is from 5mA to 15mA. In the
line hold range from 0mA to 5mA, the device is in
a power down mode and the voltage at U1 pin 37
LI (Line Input) port is reduced to a maximum of
3.5V. The DC characteristic is determined by the
voltage at U1 pin 37 LI port and R45 resistor
between U1 pin 37 LI and pin 39 LS port. It can be
calculated by the following equation: V
I
X 45.
LINE
5-16
RING DETECT
¥ U1 pin 28 (MO) is ring melody output port and
this signal drives FET3 which drive Photo coupler
U4 for artificial ring.
MF DIAL (Same as telephone section)
¥ U1 pin 2 DMS (Dial Mode Selection) port is set to
VDD by R46. It has M/B ratio of 33:66, and in no
power operation mode operates only DP.
¥ MF signal appears (tone level of low group:
typical - 14 dBm) at U1 pin 4 MFO (DTMF
Generator Output). This signal is leveled by R32,
R28 and C29, then to amplier U1 pin 9 MFI
(DTMF Amplier Input).
¥ Line dial signals appear at U1 pin 39 LS (Line
Current Sense Input).
DP DIAL (Same as telephone section)
¥ U1 pin 2 (DMS) is set to Vdd (33/66) or VSS
(40/60) by R46 or R52 resistor.
¥ Dial pulses originate at U1 pin 27 (DPN), which
toggles Q5, which drives Q2. The resulting
intermittent voltage interrupts the telephone line.
¥ Pulse M/B ratio is set by U1 pin 2 DMS port.
¥ U1 pin 35 CS port: Modulation of line voltage and
shorting the line during make period of pulse
dialling.
= V
+
LS
LI
Vdd = 33/66, and Vss = 40/60.
Samsung Electronics
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