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3CM
The NCU PCB (NCUPCB) mainly controls the connection to the telephone line. It consists of the circuits shown in the block
diagram.
The loop current detection/tone signal reception circuit IC30 detects the DC loop current formed at the DC loop/dial pulse
transmission circuit PC80 to determine the status of the telephone line. It also receives tone (DTMF) signals during remote
control. The ring signal detection circuit PC60 detects the ring signals from the telephone line to determine call reception.
The DC loop/dial pulse transmission circuit PC80 turns on and off the DC loop formed in the telephone line to send out dial
pulses (selection signals). The external telephone off-hook detection circuit (T40 and PC40) detects the off-hook state of the
1
telephone connected or the handset*
. The destination identification circuit (JP20, JP21 and JP22) is used by the fax control
PCB (FCPCB) to identify the destination of the NCU PCB (NCUPCB). The accounting pulse elimination circuit L70 removes
signals representing the communication charge information (accounting pulses) before they reach the modem when
2
telephone line is used.*
This is because accounting pulses obstruct fax communications. The ground start circuit PC10
2
requests an outside connection to the private branch exchange (PBX) when calling via the PBX.*
*1: Optional for 120 V specifications only.
*2: For 220 - 240 V specifications only.
2-2-6
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