Samsung SF6500 Service Manual page 74

5-8-2 UART Rx, Tx
TxD (Transmit Data Output) : This data signal is
transferred to CPU through ILIU chip.
RxD (Receive Data Input) : This data signal is
transferred to ILIU from CPU.
TxD
20
11
RxD
Figure 5-6 UART Tx, Rx
5-8-3 Off-Hook Detect
*EHS (Electronic Hook Switch) : This signal comes
to ILIU chip when CML relay turns on and applies
to CPU through UART Rx.
*MHS (Manual Hook Switch) : This signal comes
to ILIU chip through hook switch when the
handset is off-hooked and applies to CPU through
UART Rx.
TIP
RING
Figure 5-8 Off-Hook Detect
Samsung Electronics
5-8-4 Ring Detect
When ring signal is applied from line, this circuit
adjusts ring impedance through C19 and R26, and
eliminates the ring signal less than 18 V through
ZD2. The ring signal is outputted to RFO port.
ILIU chip counters the ring frequency and sends
out the ring melody through MO. It drives the
vcc
piezzo buzzer. The ring melody output is
transferred to CPU through photo coupler (U5).
Rx-D
TIP
vcc
Tx-D
RING
RINGER
RFO
12
MHS
13
EHS
ZD2
R29
R26
18V C21
C19
Q4
Q6
U5
D2
Figure 5-7 Ring Detect
Circuit Description
25
RFO
R30
28
MO
RING DET
5-5