Panasonic KX-TG2248S Service Manual ▷ View online
17.4. Reset Circuit
Function:
This circuit is used for to initialize the microcomputer when it incorporates an AC adaptor.
Circuit Operation:
When the AC Adaptor is inserted into the unit, then the voltage is shifted by IC100, D101 and power is supplied to the DSP.
The set can operate beyond point
in the circuit voltage diagram.
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KX-TG2248S
17.5. Locator/Intercom Mode
1. When the base unit LOCATOR/INTERCOM button is pressed, a call monitor signal (intercom sound) is output from DSP (SPP,
SPN). Thus a monitor tone is heard from the speaker.
2. At the same time, flashing of the IN USE/CHARGE (LED900) is obtained from DSP (INUSE-LED). This status is called
"Intercom stand-by".
3. The receiving signal flows:
RF
→
DSP (SPP, SPN)
→
SP
4. The transmission signal flows:
MIC
→
C235, C236
→
R213, R214
→
DSP (MIN, MIP)
→
RF
17.6. Telephone Line Interface
Telephone Line Interface Circuit:
Function
•
•
Bell signal detection
•
•
ON/OFF hook and pulse dial circuit
•
•
Side tone circuit
•
•
Auto-disconnect circuit/Parallel connection detection circuit
Bell signal detection and OFF HOOK circuit:
In the idle mode, Q4 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:
and Ring (R) leads (When the telephone rings), the AC ring voltage is transferred as follows:
T, R
→
L1, L2
→
R30, R31
→
C16, C17
→
Q6
→
DSP (BELL) [BELL]
When the CPU (DSP) detects a ring signal, Q4 turns on, thus providing an off-hook condition (active DC current flow through
the circuit) and the following signal flow is for the DC line current.
the circuit) and the following signal flow is for the DC line current.
T
→
D4
→
Q4
→
Q1
→
R5
→
D1
→
D4
→
L2
→
POS1
→
R [OFF HOOK]
ON HOOK Circuit:
Q4 is open, Q4 is connected as to cut the DC loop current and to cut the voice signal. The unit is consequently in an on-hook
condition.
condition.
Pulse Dial Circuit:
DSP (RYL) turns Q4 ON/OFF to make the pulse dialing.
Side Tone Circuit:
Basically this circuit prevents the TX signal from feeding back to RX signal.
As for this unit, TX signal feed back from Q1 is canceled by the echo canceller of DSP.
Note: DSP is IC201.
See CPU DATA (Base Unit) (P.67)
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KX-TG2248S
17.7. Auto Disconnect Circuit
Function:
This circuit is used to detect the fact that another telephone connected to the same line is OFF-HOOK while the unit is in a receiving
status or OGM transmitting status.
status or OGM transmitting status.
Circuit Operation:
The voltage DSP (DCIN1) is monitored. If a parallel-connected telephone is put into an OFF HOOK status, the presence/absence
of a parallel connection is determined when the voltage changes by 0.2V or more.
of a parallel connection is determined when the voltage changes by 0.2V or more.
When the set detects the parallel-connected telephone is OFF HOOK status, the line is disconnected.
Note:
DSP is IC201.
See CPU DATA (Base Unit) (P.67)
You can enable or disable the Auto Disconnect function.
See Check Record (P.35).
17.8. Parallel Connection Detect Circuit
Function:
In order to disable call waiting and stutter tone functions when using telephones connected in parallel, it is necessary to have a
circuit that judges whether a telephone connected in parallel is in use or not. This circuit determines whether the telephone
connected in parallel is on hook or off hook by detecting changes in the T/R voltage.
circuit that judges whether a telephone connected in parallel is in use or not. This circuit determines whether the telephone
connected in parallel is on hook or off hook by detecting changes in the T/R voltage.
It is like an “Auto Disconnect Circuit”.
Circuit Operation:
Parallel connection detection when on hook:
When the set is on hook, the voltage is monitored at DSP (DCIN0). There is no parallel connection if the voltage is 2.50 V or higher,
while a parallel connection is deemed to exist if the voltage is lower.
while a parallel connection is deemed to exist if the voltage is lower.
Parallel connection detection when off hook:
When the set is off hook, the voltage is monitored at DSP (DCIN1); the presence/absence of a parallel connection is determined
when the voltage changes by 0.2 V or more.
when the voltage changes by 0.2 V or more.
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KX-TG2248S
17.9. Calling Line Identification (Caller ID)/Call Waiting Caller ID
Function:
Caller ID
The caller ID is a chargeable ID which the user of a telephone circuit obtains by entering a contract with the telephone company
to utilize a caller ID service. For this reason, the operation of this circuit assumes that a caller ID service contract has been entered
for the circuit being used.
to utilize a caller ID service. For this reason, the operation of this circuit assumes that a caller ID service contract has been entered
for the circuit being used.
The data for the caller ID from the telephone exchange is sent during the interval between the first and second rings of the bell
signal. The data from the telephone exchange is a modem signal which is modulated in an FSK (Frequency Shift Keying) * format.
Data "1" is a 1200 Hz sine wave, and data “0” a 2200 Hz sine wave.
signal. The data from the telephone exchange is a modem signal which is modulated in an FSK (Frequency Shift Keying) * format.
Data "1" is a 1200 Hz sine wave, and data “0” a 2200 Hz sine wave.
There are two type of the message format which can be received: i.e. the single message format and plural message format. The
plural message format allows to transmit the name and data code information in addition to the time and telephone number data.
plural message format allows to transmit the name and data code information in addition to the time and telephone number data.
*: Also the telephone exchange service provides other formats.
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KX-TG2248S
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