Carrier Detection

Carrier detection while the modem is in the online state is governed by the times specified by registers S9 - Carrier Recovery Time and S10. The CD LED is the carrier detected indicator. If the carrier signal goes off, the CD LED goes off within 20 ms. If the carrier returns, the CD LED turns on within 20 ms after the carrier has been on continuously for the time specified by S9.

If the carrier remains off for the time specified by S10, then the modem hangs up. If S10 is set to 255, the time is considered to be infinite; the modem does not hang up due to loss of carrier signal.

The modem may use various algorithms to detect carrier, in addition to estimating received signal power. When any of these algorithms indicate carrier is not being received, the S9 and S10 time intervals determine when to clear the call.

See the &Cn command for RLSD behavior.

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