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LLC (Line Loss Compensation) LOOP
CURRENT DETECT
¥ The LLC is a pin option. When it is activated, the
transmit and receive gains for both I/O are
decreased by 6dB at line currents from 20mA
when the U1 pin 31 LLC is connected to AGND,
from 75mA when this pin is connected to VDD.
The LLC is deactivated when LLC pin is
connected VSS.
¥ When the CML1 relay or Hook Switch switches to
telephone line, the U1 in the LIU board and CPU
(U1) in the Main board srart communication. The
U1 send <Ack> message contains the line current
information. Using this line current information
Main CPU can recognize a parallel phone.
SERIAL INTERFACE
¥ U1 pin 11 RXD: Schmitt trigger input (treshold =
2.5V) to serial interface.
¥ U1 pin 29 TXD: Open drain output from serial
interface.
¥ The communication principle is derived from a
standard UART:
Baud Rate 9600
Start Bit 1
Stop Bit 1
Data Bits 8
Parity Bit None
LSB is transferred prior to MSB.
5-7-2. Telephone Section
RINGER CIRCUIT
¥ When a ringing signal is applied to the line, Vdd
of U1 (I-LIU) is charged up via an external path.
After Vdd has reached the operating voltage the
oscillator starts and U1 discriminates the ring
frequency.
After a valid ring frequency is applied to the U1
pin 25 RFD (Ring Frequency Discrimination) port,
the ring melody generator of U1 sends out a 3-
tone melody via the U1 pin 28 MO (Ring Melody
Output)port.
¥ U1: I-LIU and associated components.
¥ Ring frequency passes through DC blocking
capacitor C3 or C4 (for Switzerland or Austria)
and Zener-diode ZD2 or ZD3 (for Switzerland or
Austria) to U1 pin 25 RED port.
Samsung Electronics
¥ Line ring voltage passes through bridge diode
BD1, CML relay and Hook Switch to FET3 (BS170)
pin 3, C21, R19.
¥ The ring frequency discriminator of U1 assures
that only signals with a frequency between 13Hz
and 70Hz are regarded as valid ring signals.
¥ When a valid ring signal is present for 73ms
continuously, the ring melody generator (pin 28,
MO) is activated and remains active as long as a
valid ring signal is present.
¥ U1 filters the ring signals and output is pin 28
(MO).
¥ The 3 basic melody frequencies are : F1 = 880 Hz,
F2 = 1067 Hz and F3 = 1333 Hz. The repetition
rate is set to 4 which means that the sequence of
F1, F2, F3, F1, F2, F3 is repeated 4 times within a
second.
SPEECH CIRCUIT
¥ U1 (STI9510) and associated components.
¥ Handset transmitting circuit. Condensor MIC of
handset is filtered by R25, C28, C27, C20, C19,
C24, C22 and C30, and then amplified by U1 pin
32 and 33 (M1, M2)
¥ Handset receiving circuit. Receiving (Dynamic
unit) of handset is filtered by R49, C45, C40, C44
and C23, and then applied by U1 pin 1 (ROH) and
VSS.
¥ U1 pin 39 (LS) is audio output to telephone line.
SIDETONE CIRCUIT
¥ Sidetone audio characteristics are controlled by
R37, R51, R5, R26, and C41 connected to U1 pin 7
STB.
Circuit Description
5-17
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