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I have a USB modem. Is it possible to detect the phone line is busy or not?

I thought I could use AT Command to detect dial tone, but I'm not sure are there any commands support that.

Thanks.

jww
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ckmarkhsu
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2 Answers2

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I believe you have to do this the same as a human would... take it off hook and wait for dial tone.

Ripped from http://michaelgellis.tripod.com/modem.html

D alone will take the modem off-hook and wait for a dial tone. (see X command for exceptions). The length of time to wait for a dial tone before dialing is programmable in register S6.

Chris Gessler
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If you try call, and it's busy, modem send you message BUSY or NO ANSWER

Rafał Wójcik
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    thanks for you help!! My modem is just monitoring the phone line (receiving CallerID signal), so if I try call, it may disturb some users. Are there any other ways? thanks – ckmarkhsu Mar 27 '12 at 12:53