Circuit Operation:
pins 32 and 33 of IC501 Speaker.
13.15. Telephone Line Interface
Circuit Operation:
- 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 R139/R140 C139 RX
- 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.
- 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 ; thus, satisfying the
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