User`s manual

Technical Information
Pin 22 — Ring Indicator (CE)
A pulsed signal appears on this circuit when the data terminal receives an
incoming data call. This signal is maintained until the data terminal answers or
clears the call, or until the network clears the call attempt. The cadence is
designed to simulate ringing: two seconds on and four seconds off. The initial
pulse remains on for a minimum of one second.
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