Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!decwrl!fernwood!portal!cup.portal.com!dbell
From: dbell@cup.portal.com (David J Bell)
Newsgroups: sci.electronics
Subject: Re: Caller ID info wanted
Message-ID: <41214@cup.portal.com>
Date: 12 Apr 91 18:25:46 GMT
References: <41177@cup.portal.com>
Distribution: na
Organization: The Portal System (TM)
Lines: 20

More data acquired on Caller Number Delivery:

The transmission occurs during the silent interval between
the first and second power ring signals, into an *ON HOOK*
line (no load, or >100k ohms). The signal is analog, phase-
coherent, frequency-shift keying, with a logic 1 (Mark) at
1200 +/- 12 Hz, and logic 0 (Space) at 2200 +/- 22 Hz. The
transmission rate is 1200 bps, data is serial, binary,
asynchronous. Level is -13.5 dBm into 900 ohms.

Looks a lot like a Bell 202 (1200 baud) half-duplex modem!

With the interface circuit providing the demodulated serial
signal, and a UART, you have the basic interface for Caller ID.

Or, eliminate the UART and shift the level to RS-232 voltages,
and input it directly to your PC. The encoding of the number
is not clear yet, but should be easy to determine by experiment.

Dave