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of this circuit assumes that a caller ID service contract has been entered for the circuit being
used. The data for the caller ID from the telephone exchange is sent during the interval between
the first and second rings of the bell signal. The data from the telephone exchange is a modem
signal which is modulated in an FSK (Frequency Shift Keying) format. Data "0" is a 1200 Hz sine
wave, and data 1 a 2200 Hz sine wave.There are two types of the message format which can be
received: i.e. the single message format and plural message format. The plural message format
allows to transmit the name and data code information in addition to the time and telephone
number data.
9.4.2. Circuit operation
Caller ID / Caller ID signal is sent through the circuit via the following path: / TEL Line
C551,
C552
R551, R552
Pin87,88 of IC801
10. BLOCK DIAGRAM
10.1. IC801
18
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