Toshiba GD-1220, GD-1221 service manual Line 1 Current Detection Signal IC23

EU/AU/AS/C models

NCU board

					1
Line	CN3	4	Lb	R26	2

IC2

Line current

detection

IC

8 19

7 20

CN4

FAX board

	19	REVA1	66
CN262				CN5
	20	REVB1	33

MAIN board
66	160
CN5	IC23
	ASIC
33	161

Fig. 4-9

The line current detection circuit consists of the line current detection IC (IC2), ASIC (IC23) on the MAIN board, and the other peripheral devices. It detects a dial tone and the hook status of the external telephone from the current flowing through the line.

When a dial tone is input from the telephone line, current flows through the line. The line current detec- tion IC sends REVA1 and REVB1 to the ASIC as pulse signals. This allows a dial tone to be detected.

Signal Name	Type	Active	Description	Destination
REVA1	I	-	Line 1 Current Detection Signal	IC23
REVB1	I	-	Current Reverse Line 1 Current Detection	IC23
			Signal

4

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