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Ring Indicator (RI) — Pin 22
This signal remains on for the duration of the ringing signal. When a ring signal is received
by the modem, the modem automatically answers after the first ring. The modem can
answer after a specified number of rings which can be programmed in command mode, but
if none is specified, the modem answers after the first ring.
External Transmit Clock (XTC) — Pin 24
Supplies the same function as the Transmit Clock signal on pin 15.
Terminal Busy (OOS) — Pin 25
The Terminal Busy/Out of Service (OOS) circuit is not defined in the RS-232C standard, but
is used by Multi-Tech Systems and most manufacturers to make the phone lines busy to
incoming phone calls. Pin 25 is not typically connected to the RS-232C interface when
shipped from the factory; it can be ordered connected as an option. If pin 25 is connected
and is brought high, the modem is placed off hook, and is busy to incoming calls.
(From modem)
(To modem)
(To modem)
Appendix
109
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