Panasonic KX-TC1868B, Руководство по обслуживанию, Страница: 56 / 87

13.15. Telephone Line Interface
Circuit Operation:
l ANSWER
In the idle mode, Q121 is open to cut the DC loop current and decrease the ring load. When ring voltage appears at the Tip (T)
and Ring (R) leads (When the telephone rings), the AC ring voltage is transferred as follows:
T
→
L101
→
R103
→
C103
→
Q101
→
IC501 pin 64.
When the CPU (DSP) detects a ring signal, Q121 turns on, thus providing an off-hook condition (active DC current flow through the
circuit) and the following signal flow is for the voice signal.
T
→
D101
→
Q121
→
Q131
→
R138
→
C140
→
D101
→
L102
→
PO101
→
R
l
ON HOOK
Q121 is open, Q121 is connected as to cut the DC loop current and to cut the voice signal. The unit is consequently in an on-hook
condition.
l SPECIFICATIONS
In the on-hook state (idle), the current flows between the telephone line and the unit is as follows:
T
→
L101
→
R103
→
C103
→
R106
→
C104
→
R104
→
L102
→
PO101
→
R.
The DC component is blocked by C103, C104: thereby providing an on-hook condition.
The AC interface impedance is over 47 k
Ω
; thus, satisfying the telephone company requirements.
13.16. Intercom Mode
1. When the base unit LOCATOR/INTERCOM button is pressed, a call monitor signal (intercom sound) is output from pins 32 and
33 of IC501. Thus a monitor tone is heard from the speaker.
2. At the same time, flashing of the IN USE/CHARGE (LED541) is obtained from pin 65 of IC501. This status is called "Intercom
stand-by".
3. The receiving signal flows:
RF
→
pin 32 and 33 of IC501
→
SP
4. The transmission signal flows:
MIC
→
C724
→
C725
→
C726
→
R726
→
pin 47 of IC501
→
RF
56
KX-TC1868B / KX-TC1871B / KX-TC1872B