Toshiba GD-1270, GD-1260, GD-1250, GD-1160, GD-1210 Line current detection circuit, NA/TW models

4.2.4Line current detection circuit

NA/TW models

NCU board

FAX board

Line

CN10

4Lb

	R87
	1	8
		PC3
	2	7
C7
	3	6
		PC3
R86	4	5

19

CN9

20

SG

19 REVA1 2

CN501

20 REVB1 3

IC29

[IC26]

ASIC

Fig. 4-9

The line current detection circuit consists of the photocoupler (PC3), ASIC (IC29 [IC26]) on the FAX board and the other peripheral devices. It detects a dial tone and the hook status of the external tele- phone from the current flowing through the line.

When a dial tone is input from the telephone line, current flows through the line and the photocoupler is repeatedly turned ON/OFF. This allows the REVA1 and REVB1 to be the pulse signals and input to the ASIC, then the dial tone is detected.

When the handset is lifted from the external telephone, current also flows through the line and the pho- tocoupler is turned ON/OFF, then the off-hook state is detected.

Signal Name	Type	Active		Description	Destination
REVA1	I	-	Line 1	Current Detection Signal	IC29 [IC26]
REVB1	I	-	Line 1	Reverse Current Detection Signal	IC29 [IC26]

*Values in [ ] are for GD-1250/1270 in case that the descriptions vary between GD-1210 and GD- 1250/1270.

4

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