From the instruction manual for BTL.exe by Robert Glassey, G0VTQ

RTTY and the Baudot Code:

RTTY stands for Radio Teletype. On an SSB receiver it sounds like a steady 'diddle' where a tone rapidly toggles between two similar frequencies. Other digital transmissions heard on the air are mostly sent in bursts. These may be AMTOR, PACTOR, PACKET, or some other mode.

A RTTY transmission sends a character as a stream of bits. A high bit is represented by a MARK tone and a low bit is represented by a SPACE tone. Each bit is a fixed length. These tones are different frequencies, a high radio frequency for a MARK and a low radio frequency for a SPACE. If the receiver is in USB mode the audio tones will be the same way around. If LSB is used they will be reversed, ie MARK will be the lower audio tone.

Each Baudot character is made up of 7.5 bits. This is made up of 1 start bit (SPACE), 5 data bits (LSB first), and at least 1.5 stop bits (MARK). - Since Baudot is asynchronous the stop bit may be any length >1.5 bits. A new character must have a MARK before it so the start bit can be detected. The 5 data bits decode to one of two separate 'alphabets', one for letters and one for numbers and punctuation. Special codewords are used to select the alphabet, these are called Letters and Figures shifts. There are also idle (blank), space, carriage return and line feed characters.

Code  Letters  Figures Code Letters Figures LETS<->FIGS   FIGS<->LETS
===== ======   ======  ===== =      =====   = =    = =    = =    = =
00000 Blank    Blank   00001 T      5       A -    N ,    1 Q    @ F
10000 E        3       10001 Z      +       B ?    O 9    2 W    * G
01000 LF       LF      01001 L      )       C :    P 0    3 E    $ H
11000 A        -       11001 W      2       D #    Q 1    4 R    # J
00100 Space    Space   00101 H      $ ++    E 3    R 4    5 T    ( K
10100 S        '       10101 Y      6       F @    S '    6 Y    ) L
01100 I        8       01101 P      0       G *    T 5    7 U    + Z
11100 U        7       11101 Q      1       H $    U 7    8 I    / X
00010 CR       CR      00011 O      9       I 8    V =    9 O    : C
10010 D        #       10011 B      ?       J b    W 2    0 P    = V
01010 R        4       01011 G      * ++    K (    X /    - A    ? B
11010 J        BELL    11011 FIG    FIG     L )    Y 6    ' S    , N
00110 N        ,       00111 M      .       M .    Z +    # D    . M
10110 F        @ ++    10111 X      /       (Note the numbers are 'North
01110 C        :       01111 V      =       west' of the qwerty keys on
11110 K        (       11111 LET    LET     the keyboard.)

LSB of code shown                   LET Letters shift
++ @ $ * are not standardised.      FIG Figures shift   
# 'Who Are You?' request.