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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: DTMF tones
Summary: 4x4 DTMF matrix
Message-ID: <3885@kitty.UUCP>
Date: 25 Jul 90 15:57:00 GMT
References: <44900010@uxa.cso.uiuc.edu> <44900011@uxa.cso.uiuc.edu> <1990Jul25.125339.1665@focsys.uucp>
Organization: Recognition Research Corp., Clarence, NY
Lines: 32

In article <1990Jul25.125339.1665@focsys.uucp>, brad@focsys.uucp (Brad McCloy) writes:
>   I also came across some undocumented but supposedly valid tones.
> Anyone have an idea or care to guess what they do?
> Fo = 697Hz & 1633Hz
> F  = 770Hz & 1633Hz
> I  = 852Hz & 1633Hz
> P  = 941Hz & 1633Hz

	These are the DTMF tone pairs which correspond to the optional
column to the *right* of the "3-column".  The addition of these four
tone pairs creates a 4x4 matrix.  These additional tones are used for
specialized control purposes, but not, in general, to access any function
or servce provided by a telephone company; 4x4 DTMF keypads are readily
available for telephone and two-way radio use, but are no where near as
common as the conventional 3x4 DTMF keypad.

	These keys are more commonly labeled "A", "B", "C", and "D", with
"A" on the top row and "D" on the bottom row.

	The 4x4 DTMF matrix was first used with the military AUTOVON
switched voice network starting around 1963, and did not see other use
for several years.  The key designations indicated above are the AUTOVON
designations, and refer call precedence control as follows:

FO = Flash Override	highest call precedence; nudet on the horizon :-)
F  = Flash traffic
I  = Immediate traffic
P  = Priority traffic

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
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