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6-2. I/F for Telephone line
This chapter is for an interface (I/F) to connect with telephone line and there are 4 I/Fs for 4 lines
(Line 1-4) on IT-M804/M704.
I/F for Line 1, 2, 3, and 4 are similar circuit, but Line 1 has control data/circuit for extension call.
One DATA PORT is equipped and the line which DATA PORT being connected is selectable by
switch.
I/F for telephone line is made up of following circuits.
1
Protection circuit for SURGE/NOISE The circuit is composed of 400V Surge absorber (SG101,
2
Telephone BELL (Ringer) detection
circuit
Circuit that detects BELL signal
from telephone company under
on-hook condition.
3
Holding circuit
Circuit to make holding
telephone line.
4
Line Selection and LOOP circuit
5
IN USE detection circuit
This is a circuit for detecting line
in use.
SG201, SG301, SG401) and noise filter (T100,T200,T300,T400).
This circuit consists of CRs (C101,R01,C201,R201,C301,R301,
C401,R401) for coupling in order to pick alternating current signal
and PHOTO COUPLER(PH101,PH201,PH301,PH401) which is
possible to perform alternating current operation.
BELL signal is inputted into PORT of CPU through this PHOTO
COUPLER.
This circuit consists of PHOTO COUPLER (PH902,PH903,
PH904) for separating primary and secondary and TRs
(transistor/Q905,Q906,Q907,Q908) and resisters (R916,R926,
R936,R946) which made up LINE LOOP. But RELAY (RY-5) is
used only on LINE-1.
When PHOTO COUPLER or TR(Q910) for driving relay is turned
on by PORT on CPU, TR (902,Q903,Q904) or RELAY (RY-5) is
turned on, and CIRCUIT LOOP current flows through resistors
(R916,R926,R936R,R946)
TRs(Q905,Q906,Q907,Q907), and line holding is performed.
This circuit consists of DIODE BRIDGE (DB101,DB201,DB301,
D401) on each line, RELLAY(RY1,RY2,RY3,RY4) for connecting
to the line, TRs (Q601,Q602) for circuit LOOP, PHOTO
CUPPLER (PH601) and AF TRANSFORMER (T600) to
separate primary from secondary.
Telephone line is connected to LINE LOOP circuit through DIODE
BRIDGE and RELAY being set to MAKE by control of CPU.
On LINE LOOP circuit, LINE LOOP current flows with keeping
AC high impedance for reactance circuit by the transistor.
Calling signal is afterwards connected to SPEECH N/W (network)
circuit via AF TRANSFORMER.
DP DIAL is made here. Photo Coupler (PH601) is controlled by
CPU port and TR(Q601) connected with the relay for connection
to Line is made turning on and off, then dial pulse signal is made
and transmitted to the line.
Line voltage passing through DIODE BRIDGE is detected by OP
AMP(IC101) under high impedance operation and sent to CPU.
CPU makes a judgement that the line is used.
connected
to
EMITTER
of
26
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