Serial Interface - Samsung SF4300C Service Manual

5-2-5 Line Current Detector
¥ When CML1 relay connects telephone line, U3(STI9510) of LIU board and MFP controller of the main board
(U15:KS32C6200) start communication through UART. U3 of LIU board sends signal that includes infor-
mation of line current value, whenever it receives orders or data from U15 of the main board.

5-2-6 Serial Interface

¥ This part does serial communication with MFP controller of the main board (MAIN PBA:U15) that controls
the whole system. It controls LIU by giving and taking all control orders and line status.
¥ U3-11 RXD : Schmitt Trigger input, Receiving terminal..
¥ U3-29 TXD : Open Drain output terminal
¥ Standard UART communication
- Baud Rate : 9600bps
- Start, Stop bit : 1bit each
- Data bits : 8 bit
- Parity bit : none
5-2-7 MAJOR FUNCTIONS OF PARTS
1) U3 : STI9510
- Key part of LIU board. Speech Network, Dialer, Ringer and UART are built in one IC package.
2) U5 : PC817
- Photo coupler. It enables UART of U3(STI9510) to receive control signal or dialing information from
MFP controller of the main board (U15).
- Insulation between prinary and secondany circuit part.
3) U6 : PC817
- Photo coupler. It enables UART(U3-29:TXD) of U3(STI9510) to deliver telephone line status or
response signal about control signal or dialing information from LIU to MFP controller of the main
board (U15).
- Insulation between prinary and secondany circuit part.
4) U4 : PC817
- It senses and delivers ring signal to the main board.
- Insulation between prinary and secondany circuit part.
5) U2 : PC814
- It senses hook-off (Line connection) of the external telephone and delivers it to the main board.
- Insulation between prinary and secondany circuit part.
6) BD1 : BRIDGE DIODE
- Regardless of the polarity of DC power from telephone line, the voltage put out on Pin.1 has always
+ polarity against pin Pin.2. So DC loop forms always in the same direction regardless of the polar-
ity of the telephone line.
7) T2,T3 : TRANSFORMER
- It delivers signals from the telephone line to modem or signals from modem to the telephone
line.
- Insulation between prinary and secondany circuit part.
Samsung Electronics 5-29