BAUDOT RADIOTELETYPE....

One of the first data communications codes to receive widespread use had five
information pulses (or levels) to present the alphabet, numerals, symbols and
machine functions. In the United States, the current five-level code is
commonly called the Baudot code. There are many variations in five-level
coded character sets, principally to accommodate foreign-language alphabets.
Current FCC rules in 97.69(a) identify the Baudot code as the International
Telegraph Alphabet Number 2 (ITA2). As the ITA2 is a five-level code, and there
are only two conditions for each level (A or Z, space or mark, binary 0 or 1).
Therefore, a total of 2 x 2 x 2 x 2 x 2 = 2(5) = 32 different code combinations
are possible. Because it is necessary to provide 26 latin letters, 10 numerals
and punctuations, the 32 code combinations are not sufficient. THis was solved
by using the codes twice; once in the letters (LTRS) case and again in the
figures (FIGS) case. Two special characters, LTRS and FIGS are used to indicate
whether subsequent characters will be in letters or figures case. The receiving
terminal stores the last received LTRS or FIGS character so it remaines in the
last-received case until changed. Control functions such as LTRS, FIGS, carriage
return (CR), line feed (LF), space (SP) and blank are assigned to both the
letters and figure cases so that they can be used in either case. The remaining
26 code combinations have different character meaning, depending on whether
preceded by LTRS or FIGS characters.

MARK  = 1   L = LETTER CASE
SPACE = 0   F = FIGURE CASE

                    U.S.     ITA2
5 4 3 2 1  Hex   L   F
---------   --   -----     |
0 0 0 1 1 = 03 = A   -     | -
1 1 0 0 1 = 19 = B   ?     | ?
0 1 1 1 0 = 0E = C   :     | :
0 1 0 0 1 = 09 = D   $     | unassigned    NOTE 1
0 0 0 0 1 = 01 = E   3     | 3
0 1 1 0 1 = 0D = F   !     | unassigned    NOTE 1
1 1 0 1 0 = 1A = G   &     | unassigned    NOTE 1
1 0 1 0 0 = 14 = H   #     | unassigned    NOTE 1, 2
0 0 1 1 0 = 06 = I   8     | 8
0 1 0 1 1 = 0B = J   '     | BELL          NOTE 1
0 1 1 1 1 = 0F = K   (     |
1 0 0 1 0 = 12 = L   )     |
1 1 1 0 0 = 1C = M   .     |
0 1 1 0 0 = 0C = N   ,     |
1 1 0 0 0 = 18 = O   9     |
1 0 1 1 0 = 16 = P   0     |
1 0 1 1 1 = 17 = Q   1     |
0 1 0 1 0 = 0A = R   4     |
0 0 1 0 1 = 05 = S   BELL  | '             NOTE 1
1 0 0 0 0 = 10 = T   5     |
0 0 1 1 1 = 07 = U   7     |
1 1 1 1 0 = 1E = V   =     | ;             NOTE 1
1 0 0 1 1 = 13 = W   2     |
1 1 1 0 1 = 1D = X   /     |
1 0 1 0 1 = 15 = Y   6     |
1 0 0 0 1 = 11 = Z   "     | +             NOTE 1
0 1 0 0 0 = 08 = (CR)   CARRIAGE RETURN
0 0 0 1 0 = 02 = (LF)   LINE FEED
1 1 1 1 1 = 1F = (LTRS) LETTERS SHIFT
1 1 0 1 1 = 1B = (FIGS) FIGURES SHIFT
0 0 1 0 0 = 04 = (SP)   SPACE
0 0 0 0 0 = 00 = (BLK)  BLANK

NOTE 1:     These Figure case characters are used for international Baudot.
            (ITA2)
NOTE 2:     Also motor stop.

Baudot Signaling Rates and Speeds.

 Signaling     Data         Stop
 Rate          Pulses       Pulse      Speed      Common
 (bauds)       (ms)         (ms)       (WPM)      Name
 45.45         22.0         22.0       65.00      Western Union
               22.0         31.0       61.33      "60 Speed"      (NOTE 3)
               22.0         33.0       60.61      45 Baud
 50.00         20.0         30.0       66.67      European 50 bauds
 56.92         17.57        25.0       76.68      "75 Speed"
               17.57        26.36      75.89      57 bauds
 74.20         13.47        19.18     100.00      "100 Speed"
               13.47        20.21      98.98      74 bauds
100.00         10.00        15.00     133.33      100 bauds

NOTE 3:     Most common TTY Baudot.

The BAUD is a unit of signaling speed equal to one pulse (event or sysnol) per
second. The signaling rate in bauds can be found by deviding the shortest pulse
length into one; for example, 1/0.022 = 45.45, commonly abbreviated to 45.5 or
even 45 bauds.

Time sequence of typical Baudot character, the letter D.

MARK --------.    .----.    .    .----.    .--------.
(CURRENT)    |    |    |    .    |    |    |        |
   (ON)      |    |    |    .    |    |    |        |
             |    |    |    .    |    |    |        |
             |    |    |    .    |    |    |        |
             |    |    |    .    |    |    |        |
SPACE        '----'    '----'----'    '----'        '----
(CURRENT)         | b0   b1   b2   b3   b4 |   ^
   (OFF)       ^  | (m)  (s)  (s)  (m)  (s)|   '
               '      DATA PULSES FOR 'D'      '
               '                               '
               '                               '
               '                               '
          START PULSE                     STOP PULSE


