Panasonic KX-FT21RS - Manual (Page 130)

6.8. NCU SECTION
6.8.1. GENERAL
This section is the interface between the telephone line and external telephone. It is composed of an EXT. TEL Line relay (RLY1),
bell detection circuit, EXT TEL selection circuit, pulse dialing circuit, line amplifier, sidetone circuits and multiplexer.
6.8.2. 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.
[IC1 (99) High Level
→
CN9 (8)]
→
CN102 (8)
→
Q2 ON
→
RLY1 (make)
6.8.3. BELL DETECTION CIRCUIT
1. Circuit Operation
The signal waveform for each section is indicated below. The signal (low level section) input to pin 56 of ASIC IC1 on the digital
board is read.
TEL LINE
→
PC5 (1, 2 - 4)
→
PC102(6)
→
[CN9(6)
→
R19
→
IC1(56)]
6.8.4. PULSE DIALIG
[IC1 (28) High Level
→
CN10 (4)]
→
CN202 (4)
→
Q3 ON
→
PC1 ON (make)
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KX-FT21RS