Samsung sf150t Service Manual page 40

Serial interface
¥ U201 pin 11 RXD:
(threshold = 2.5V) to serial interface.
¥ U201 pin 29 TXD: Open drain output from serial
interface.
¥ The communication is standard UART :
Baud Rate 9600
Start Bit 1
Stop Bit 1
Data Bits 8
Parity Bit None
LSB is transferred prior to MSB.
5-6-2 Telephone Section
RINGER CIRCUIT
¥ When a ringing signal is applied to the line, Vdd
of U201 (I-LIU) is charged via an external path.
After Vdd has reached the operating voltage the
oscillator starts and U201 detects the ring
frequency.
After a valid ring frequency is applied to the
U201 pin 25 RFD (Ring Frequency
Discrimination) port, the ring melody generator
of U201 sends out a 3-tone melody via U201 pin
28 MO (Ring Melody Output) port.
¥ U201: I-LIU and associated components.
¥ Ring frequency passes through DC blocking
capacitor C206 (C205 for Switzerland or Austria)
and Zener-diode ZD205 (ZD209 for Switzerland
or Austria) to U201 pin 25 RFD port.
¥ Line ring voltage passes through DC blocking
capacitor C201, current limit resistor R205,
bridge diode BD201, CML relay, and Hook
Switch to FET201 (BS170) pin 3, C214, ZD203
and R246.
¥ The ring frequency discriminator of U201
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 at least
73ms, the ring melody generator (pin 28, MO) is
activated and remains active as long as a valid
ring signal is present.
¥ U201 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
F!, F2, F3, F1, F2, F3 is repeated 4 times within a
second.
SF150T
Schmitt trigger input
Speech Circuit
¥ U201 (STI9510) and associated components.
¥ Handset transmitting circuit: Handset
transmitter audio (Condensor MIC.) is filtered
by R240, C232, C224, C225, C226, C227, C229 and
C230, and then amplified by U201 pin 32 and 33
(M1, M2).
¥ Handset receiving circuit: Handset receiver
(Dynamic unit) is filtered by R229, C241, C209,
C203 and C231, and then applied to U201 pin 1
(ROH) and VSS.
¥ U201 pin 39 (LS) is audio output to telephone
line.
Sidetone Circuit
¥ Sidetone audio characteristics are controlled by
R238, R235, R237, R239, and C202 connected to
U201 pin 7 STB.
Circuit Description
5-9