Line Current Detect Circuit - Toshiba e-STUDIO170F Service Manual

7.4.3

Line Current Detect Circuit

US/CA models
NCU PBA
C7
R86
Lb
4
Line
The line current detect circuit consists of the photo-coupler (PC3), ASIC (I/O port: IC38) on the Main
PBA, and 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 and the photo-coupler
repeats turning on and off. This allows the REVA and REVB to be pulse signals and input to the ASIC to
detect the dial tone.
When the handset is lifted from the external telephone, current also flows through the line and the
photo-coupler turns on and off to detect the off-hook status.
Signal Name Type
REVA I
REVB I
January 2005 © TOSHIBA TEC
R87
1 8
PC3
2 7
3 6
PC3
4 5
SG
Fig.7-41
Active Description
- Line current detect signal
- Current reverse line current detect signal
7 - 59
Main PBA
REVA
19 19 36
REVB
20 20 37
Destination
ASIC
ASIC
e-STUDIO170F Circuit Description
IC38
ASIC
( I/O port )
7