CIRCUIT OPERATIONS
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KX-FT21LA
6. NCU Section
6-1. GENERAL
This section is the interface between the telephone line and external telephone. It is composed of an EXT. TEL Line re-
lay (RLY1), bell detection circuit, EXT TEL selection circuit, pulse dialing circuit, line amplifier, sidetone circuits and mul-
tiplexer.
6-2. Line relay (RLY1)
(1) Circuit Operation
Normally, this relay switches to the external telephone side (break) and switches to the open side (make) when the unit
starts facsimile communication. Pulse dialing is also performed by ON/OFF of the relay.
6-3. BELL DETECTION CIRCUIT
(1) Circuit Operation
The signal waveform for each section is indicated below. The signal (low level section) input to pin 19 of ASIC IC4 on the
digital board is read.
Between the Tip and Ring
Between PC1 (1) and (2)
PC1 (4) /Gate Array IC1 (56)
TEL LINE PC1 (1, 2-4) IC1 (56)
about 150V
0V
1.5V
1.5V
5V
48V
[IC1(99) High Level CN2 8 ] CN1 8 Q3 ON RLY1(make)
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