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Reset Signal is outputted from IC7 and inputted into IC2,
IC3 and IC6 at the connection of TEL cord.

This circuit converts the voltage supplied from PBX into the power supply voltage of +3.3V by IC1 (Switching Regulator IC).
Q22 and Q23 control the power supply circuit as below to turn IC1 on in low consumption current at starting up.

• Input Voltage  approx. 26V or less 

→Q23 OFF →Q22 ON →IC1-pin 3 H →IC1 OFF

• Input Voltage  approx. 26V or more 

→Q23 ON →Q22 OFF →IC1 ON

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The data communication circuit serves the following functions:
Information exchanger between PBX and proprietary telephone, key input information as well as data for the LED control, LCD
control, voice data, etc.  This information is continuously exchanged at all times.

The data received from PBX is inputted to the comparator (pin 36) built in IC2  through Pulse Trans T1.  The threshold voltage of
the comparator is determined by R101 to 103 and inputted to pin 37 and 35 of IC2.
The data to PBX is outputted from pin 38 and 39 of IC2, drives T1 by Transistor Q1 and transmitted.

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This circuit performs the same communication as DXDP-compatible DPT and PBX communication connected with DXDP port.

The data to Slave DPT is outputted from pin 33 and 34 of IC2 and sent by Transistor Q2 and Q3.
The data from Slave DPT is inputted to the comparator (pin 31) built in IC2.
The threshold voltage of the comparator is determined by R112 to 114 and inputted to pin 30 and 32 of IC2.
Also, the supplying power to Slave DPT is controlled by a constant current circuit of Q16 as below.

•IC2-pin 28 as H : Constant current circuit ON
•IC2-pin 28 as L : Constant current circuit OFF
•IC2-pin 29 as H : 40mA Feeding (Slave DPT usually)
•IC2-pin 29 as L : 20mA Feeding (Slave DPT at starting up only)

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This circuit performs the setting of the call path/vol. adjustment in each call mode by IC4.
The audio gain of each call is determined by download data from PBX.

• IC2 sends each audio data to IC3 by PCM interface.
• IC2 receives each audio data from IC3 by PCM interface.

1. Handset Call

Transmitting signal is inputted from handset microphone and amplified by IC4 built-in Amp 

→ A/D conversion →Gain adjust-

ment by IC4 

→inputted to IC3 and IC2 in PCM data →then sent to PBX.

Receiving signal is inputted from PBX 

→IC2→IC3→D/A conversion after the input to IC4 in PCM data→Gain adjustment by

DSP of IC4

→Pin 26 of IC4→ outputted from Q51 to handset.

2. Speakerphone Call

The speakerphone mode can only provide a one-way communication path.
IC3 compares transmitting signal and receiving signal during speakerphone mode, then provide a one-way communication
path.

Transmitting signal is inputted from SP phone mic. and amplified by IC4 built-in Amp

→ A/D conversion→inputted to IC3 in

PCM data

→Gain adjustment by IC3→inputted to IC2→ then sent to PBX.

Receiving signal is inputted from PBX is 

→IC2→Gain adjustment by IC3 →inputted to IC4 in PCM data→D/A conversion→pin

24 of IC4

→pin 27 of IC4→pin 28 of IC4→pin 29 of IC4→ outputted from pin 3 and 4 of IC4 to speaker.