Ring Indicator (RI) - pin 22
Ring Indicator indicates a ringing signal on the telephone line. When
the modem is off hook or in an analog loopback test (&T1 or &T8), RI
is off. If the modem is in the idle state and a valid ring signal is detected,
RI comes on within 300 ms after initial signal detection and remains on
until the signal stops (no more than 50 ms).
If &Q4 (Hayes AutoSync) is in effect, and the online state is active, RI
goes off when the end of frame byte is transmitted and the transmitter is
entering the idle state. RI goes high when the DTE (application) sends the
next byte of data to the modem.
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