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• DPT data communications

Bch/Dch/Cch data  is  transmitted  from  the  DTL/DTH  terminal  of  ASIC,  and  the  AMI-converted  pulse  signal  is  output  to
DPT (between D1 and D2) by way of the driver U303 and the pulse transformer T300. 
ASIC compares VREF+ and VREF- with the input wave- form, and receives a valid pulse.

• Bch communications

Communicated by the PCM data (64kbps x 2) connected from the local highway by ASIC.
Used mainly for the audio signal of DPT.

• Dch communications

Communicated by the data (16kbps) protocol-converted by the HDLC controller in ASIC.
Used mainly for the control signal of DPT.

• Cch communications

Communicated by the data (8kbps) converted by the serial/parallel-converting circuit in ASIC.
Used mainly for recognizing the terminal model.

• PT current-supply circuit

+40V is superimposed on the transmit/receive data line (D1, D2), and fed to PT. Supply voltage is +40V for new DPT. It will be
switched after the connected PT is judged through communications. I/O control is as follows.

C302A

R322A

C304A

R319A

T300A

1

2

4

5

6

7

10

9

8

C305A

R312A

R317A

R314A

DG

R318A

R315A

DG

C303A

+3.3V

C301A

C300A

DG

R313A

U303A

2

6

1

R316A

U303A

5

3

4

R325A

R326A

C323A

C324A

DR[0]

DTH[0]

DTL[0]

D1

D2

DG

R300A

R301A

R305A

R307A

ZNR301A

T300A

1

2

4

5

6

7

10

9

8

+3.3V

C306A

DG

R304A

+40V

U302A

5

3

4

DG

DG

FG

R302A

1

2

3

4

6

5

7

8

U301A

47k

5

3

4

D303A

DG

R310A

U301A

47k

2

6

1

R306A

ZNR300A

R311A

+3.3V

PT_POW[0]

C301A

D301A

+40V

DG

Q300A

B

E

C

C300A

U302A

2

6

1

R308A

D300A

R303A

DG

R309A

PT_CUR[0]

U300AB

2

6

1

D1

D2

10

Power supply is 40V only.
40V20mA and 40V80mA constant-current circuits by Q300, U302, R307, and R310 are used.
The following is the flow chart of telephone switching at boot-up.

PT_POW

PT_CUR

H

H

0V

H

L

0V

L

H

40V80mA

L

L

40V20mA

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The input from the main power supply is in 2 voltage levels: +3.3V, +40V.
Power supply block diagram is described as below figure.

12