Toshiba DP120F, Service Manual

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DP120F/DP125F Circuit Description 7-84 March 2000 © TOSHIBA TEC
EU/AU/ASIA/HK models
The line current detection circuit consists of the line current detection IC (IC2), 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. The line
current detection IC sends the OREVA1 and OREVB1 to the I/OP-1 GA as pulse signals. This
allows a dial tone to be detected.
When the handset is lifted from the external telephone, current also flows through the line and
the line current detection IC turns on and off to detect the off-hook status.
Fig. 7-4-8
07-04-03E
Signal Name Type Active Description Destination
OREVA1 I - Line 1 Current Detect Signal I/OP-1 GA
OREVB1 I - Current Reverse Line 1 Current Detect I/OP-1 GA
Signal