KX-TDA6381X, KX-TDA6381SX - Panasonic PBX Service Manual (repair manual). Page 13

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This is detected by the photo coupler (pin 4 of PC4) at part of making DC loop. PC4 4-pin is High level during a call. However, at
end-call, PC4 4-pin converts from High to Low.
It detects an end-call with measuring of the signal width of Low level by CODEC (e.g. pin 35 of IC6, CPCDET).
The available setting values for detection width are none, 0.5msec~8msec(at 2msec intervals) and 16~896msec(at 8msec inter-
vals).

Configured by the photo couplers (PC1, PC2) that enable to detect each current in Tip

Ring, RingTip direction. (PC2 is used

in common as the bell detection photo coupler). Using Software, it stores the current direction (the detected photo coupler) at
acquiring line and recognizes the action by changing of the current direction (the detected photo coupler changes).

When the current flows in the direction of Ring to Tip, 4-pin of PC1 is Low and 4-pin of PC2 is High.

•  Ring

L1R2PC1(1-2)D3RL3Q4(C-E)D4D3L1TH1Tip

When the current direction (polarity) is reversed from Tip to Ring, 4-pin of PC1 turns to High and 4-pin of PC2 turns to Low. 
It recognizes the action by changing of the current direction (the detected photo coupler changes).

•   Tip

TH1L1D3D4Q4 (C-E)RL3D3PC1 (1-2)R2L1Ring

AG

+5V

DG

+5V

+5V

R

20A

PC5A

1

2

3

4

R

17A

T1A

2

1

3

4

C8A

D4

A

R

11A

R

14A

R15A

R16A

R

18A

R

19A

PC

4

A

1

2

3

4

C6

A

C7A

Q5A

E

C

B

ZN

R

2

A

RL3A

4

3

2

1

D5

A

Q4A

E

C

B

CODEC

IC6

R[0]

T[0]

AG

+5V

DG

DG

DG

DG

DG

+5V

+5V

+5V

+5V

+5V

SFG

R

20A

PC5A

1

2

3

4

R

17A

D2A

R3

A

T1A

2

1

3

4

C1

A

C2

A

C4

A

C8A

D1A

D4

A

R21A

R

11A

R

14A

R15A

R16A

R1

8

A

R

19A

R1

A

R22A

R2

A

R4A

1.2K

R5

A

R6

A

J1A

RL

2

A

4

3

2

1

J4A

PC1A

1

23

4

PC2A

1

2

3

4

PC

4

A

1

2

3

4

L1A

1

2

3

4

C3

A

CN3 2

CN3 3

J7

A

C6

A

C7A

Q5A

E

C

B

ZN

R

2

A

CN2

1

26

D3A

1

2

3

4

TH1A

ZN

R

1

A

RL3A

4

3

2

1

D5

A

SA

1

A

12

3

Q4A

E

C

B

A

Ring

Tip