Line Current Detect Circuit - Toshiba DP120F Service Manual

4.3 Line Current Detect Circuit

US/CA/TW models
The line current detect circuit consists of the photo-coupler (PC3), I/OP-1GA (IC7) 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 OREVA1 and OREVAB1 to be pulse signals
and input to the I/OP-1 GA 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
OREVA1 I
OREVB1 I
March 2000 © TOSHIBA TEC
Fig. 7-4-7
Active
- Line 1 Current Detect Signal
- Line 1 Current Reverse Current Detect
Signal
Description
7-83
Destination
I/OP-1 GA
I/OP-1 GA
DP120F/DP125F Circuit Description
07-04-03