Hello Jasen,

JB> what does C represent in a dial string?

JB> my modems generate a tone for the C
JB> does anyone know what that tone is for?

Yes, that is very simple.
The complete DTMF TondeDial sequence also supports 4 extra digits to dial.
It is a matrix from 4 by 4 positions.

ITU-T (was CCITT) V19  DTMF  /-< Not allways used, or not present on phonekeys.
                             |
       Hz   1209 1336 1477 1633
       697    1    2    3    A
       770    4    5    6    B
       852    7    8    9    C
       941    *    0    #    D

DTMF = Dual Tone Multi Frequency

You can use all the DTMF characters including the extra DTMF characters (ABCD)
for controlling hardware remotely with a "password". I.e. to turn on your
Central Heating from 15 oC to 21 oC an hour before you arrive at home. In that
case you donot like others to manage your heating costs for example ;-(.
As most phones only supports 1234567890*# and not the ABCD ones, using one of
the latter gives more security in the password. You then have to use a manual
dialler with these ABCD codes on it, or use a modem.
Beware that not all (old an/or new) modems supports all the DTMF characters
(including ABCD) in the dial$tring!
So you have to switch on the sound and listen, (if you can ;-).

In the Netherlands (Europe) DTMF is also used for the TextTelephone systems for
the DEAF people to "talk" to each other.
Special DTMF-modems are used to convert DTMF tones to a DTMF charater and after
that to convert a string of characters to an ASCII character.
The Star * and Hash # -characters are used as a single or multiple prefix.

StarHash table for TextTelephone for the DEAF in the Netherlands (Europe):

  DTMF-  ASCII-    ASCII-
  Code   Character Value

    * 0  BS       008      Cursor 1 position back
  * * 9  CR+LF    013+010  New Line
      0  Space    032
# # # 0    !      033
           "      034
           #      035
           $      036
  * * 5    %      037
           &      038
           '      039
  * * 6    (      040
  * * 7    )      041
           *      042
  * * 1    +      043
  * * 8    ,      044
  * * 2    -      045
    # 9    .      046
           /      047
  * # 0    0      048
  * # 1    1      049
  * # 2    2      050
  * # 3    3      051
  * # 4    4      052
  * # 5    5      053
  * # 6    6      054
  * # 7    7      055
  * # 8    8      056
  * # 9    9      057
  * * 4    :      058
# # # 9    ;      059
           <      060
  * * 3    =      061
           >      062
    # 0    ?      063
           {at}      064
# # * 1    A      065
  # # 1    B      066
# # # 1    C      067
# # * 2    D      068
  # # 2    E      069
# # # 2    F      070
# # * 3    G      071
  # # 3    H      072
# # # 3    I      073
# # * 4    J      074
  # # 4    K      075
# # # 4    L      076
# # * 5    M      077
  # # 5    N      078
# # # 5    O      079
# # * 6    P      080
  # # 6    Q      081
# # # 6    R      082
# # * 7    S      083
  # # 7    T      084
# # # 7    U      085
# # * 8    V      086
  # # 8    W      087
# # # 8    X      088
# # * 9    Y      089
  # # 9    Z      090
           [      091
           \      092
           ]      093
           ^      094
           _      095
           `      096
    * 1    a      097
      1    b      098
    # 1    c      099
    * 2    d      100
      2    e      101
    # 2    f      102
    * 3    g      103
      3    h      104
    # 3    i      105
    * 4    j      106
      4    k      107
    # 4    l      108
    * 5    m      109
      5    n      110
    # 5    o      111
    * 6    p      112
      6    q      113
    # 6    r      114
    * 7    s      115
      7    t      116
    # 7    u      117
    * 8    v      118
      8    w      119
    # 8    x      120
    * 9    y      121
      9    z      122
           {      123
           |      124
           }      125
           ~      126
    * 0  Delete   127
           {at}      128

If no DTMF-$tring is given, than that ASCI-character is not available on the
TextTelephone for the DEAF.

Sent DTMF (all modems):
AT X0 M3 L3 S7=1 S10=255 S11=55
ATDT  ;

Beware of the limit of 40 chararters in the dial$tring.

To transmit the text:
The quick brown fox jumps over the lazy dog.
THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG.

to a Dutch TextTelephone, you have to send:

AT X0M3L3S7=1S10=255S11=55
ATDT ##73206#7#3#1401#6#5850#2#5#80;
ATDT *4#7*5*6*70#5*82#607320#4*19*9;
ATDT 0*2#5*3#9**9##7##3##20##6###7#;
ATDT ##3###1##40##1###6###5##8##50#;
ATDT ##2###5###80##*4###7##*5##*6##;
ATDT *70###5##*8##2###60##7##3##20#;
ATDT ##4##*1##9##*90##*2###5##*3#9;

The other way round is also possible.
For instance when you call a TextTelePhone and the Deaf person is not at home,
his phone may send you an answer text. With a DTMF decoder (e.g. a voice modem)
you can receive that DTMF-characters and convert them with (selfmade) software
to readable ASCII-text.

To receive DTMF in VoiceMode with Rockwell modems:
AT #CLS=8
The DTMF charaters have the format:  .
 = Data Link Escape = decimal 10 = CTRL P.
You may skip or delete this code from your inputstream.
When  b
receives your terminal program, then the phone-line is Busy and you have to
hang up with ATH0.
After that again an AT#CLS=8  is needed to receive the next DTMF call from
anyone.
With a local PBAX you can test and experiment without external costs.
Hope you understand DTMF (coding) now better?
Best wishes for 2003.

Greetings from: |_|     |\
                | |enri |/erksen, SysOp UniCorn BBS, Arnhem NL +31-26 4425506.
Connectivity:
TextTelephone: +31-(0)26-secret  ITU-T V19 = DTMF (for the DEAF), NO Voice.
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UniCorn BBS    +31-(0)26-4425506 Modem  8N1, + ErrorCorrection/DataCompres.
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