The printable characters go from 00100000 to 01111110, where 00000000 through 00011111 and 01111111 are non-printable characters that convey other information. The printable characters are:

                    0000 0001 0010 0011  0100 0101 0110 0111   1000 1001 1010 1011  1100 1101 1110 1111
           0010nnnn       !    "    #     $    %    &    '      (    )    *    +     ,    -    .    /
           0011nnnn  0    1    2    3     4    5    6    7      8    9    :    ;     <    =    >    ?
           0100nnnn  @    A    B    C     D    E    F    G      H    I    J    K     L    M    N    O
           0101nnnn  P    Q    R    S     T    U    V    W      X    Y    Z    [     \    ]    ^    _
           0110nnnn  `    a    b    c     d    e    f    g      h    i    j    k     l    m    n    o
           0111nnnn  p    q    r    s     t    u    v    w      x    y    z    {     |    }    ~

where 00100000 is a space character. You are not required to memorize any specific characters.

A full table with both printable and non-printing control characters is provided here:

Dec Hex  Oct  Char                             Dec Hex  Oct   Char    Dec Hex  Oct  Char    Dec Hex  Oct  Char
  0 0x00 0000 NUL (null)                        32 0x20 0040 Space     64 0x40 0100  @       96 0x60 0140  `
  1 0x01 0001 SOH (start of heading)            33 0x21 0041   !       65 0x41 0101  A       97 0x61 0141  a
  2 0x02 0002 STX (start of text)               34 0x22 0042   "       66 0x42 0102  B       98 0x62 0142  b
  3 0x03 0003 ETX (end of text)                 35 0x23 0043   #       67 0x43 0103  C       99 0x63 0143  c
  4 0x04 0004 EOT (end of transmission)         36 0x24 0044   $       68 0x44 0104  D      100 0x64 0144  d
  5 0x05 0005 ENQ (enquiry)                     37 0x25 0045   %       69 0x45 0105  E      101 0x65 0145  e
  6 0x06 0006 ACK (acknowledge)                 38 0x26 0046   &       70 0x46 0106  F      102 0x66 0146  f
  7 0x07 0007 BEL (bell)                        39 0x27 0047   '       71 0x47 0107  G      103 0x67 0147  g
  8 0x08 0010 BS  (backspace)                   40 0x28 0050   (       72 0x48 0110  H      104 0x68 0150  h
  9 0x09 0011 TAB (horizontal tab)              41 0x29 0051   )       73 0x49 0111  I      105 0x69 0151  i
 10 0x0a 0012 lF  (line feed)                   42 0x2a 0052   *       74 0x4a 0112  J      106 0x6a 0152  j
 11 0x0b 0013 VT  (vertical tab)                43 0x2b 0053   +       75 0x4b 0113  K      107 0x6b 0153  k
 12 0x0c 0014 NP  (new page)                    44 0x2c 0054   '       76 0x4c 0114  L      108 0x6c 0154  l
 13 0x0d 0015 CR  (carriage return)             45 0x2d 0055   -       77 0x4d 0115  M      109 0x6d 0155  m
 14 0x0e 0016 SO  (shift out)                   46 0x2e 0056   .       78 0x4e 0116  N      110 0x6e 0156  n
 15 0x0f 0017 SI  (shift in)                    47 0x2f 0057   /       79 0x4f 0117  O      111 0x6f 0157  o
 16 0x10 0020 DLE (data link escape)            48 0x30 0060   0       80 0x50 0120  P      112 0x70 0160  p
 17 0x11 0021 DC1 (device control 1)            49 0x31 0061   1       81 0x51 0121  Q      113 0x71 0161  q
 18 0x12 0022 DC2 (device control 2)            50 0x32 0062   2       82 0x52 0122  R      114 0x72 0162  r
 19 0x13 0023 DC3 (device control 3)            51 0x33 0063   3       83 0x53 0123  S      115 0x73 0163  s
 20 0x14 0024 DC4 (device control 4)            52 0x34 0064   4       84 0x54 0124  T      116 0x74 0164  t
 21 0x15 0025 NAK (negative acknowledgement)    53 0x35 0065   5       85 0x55 0125  U      117 0x75 0165  u
 22 0x16 0026 SYN (synchronous idle)            54 0x36 0066   6       86 0x56 0126  V      118 0x76 0166  v
 23 0x17 0027 ETB (end of transmission block)   55 0x37 0067   7       87 0x57 0127  W      119 0x77 0167  w
 24 0x18 0030 CAN (cancel)                      56 0x38 0070   8       88 0x58 0130  X      120 0x78 0170  x
 25 0x19 0031 EM  (end of medium)               57 0x39 0071   9       89 0x59 0131  Y      121 0x79 0171  y
 26 0x1a 0032 SUB (substitute)                  58 0x3a 0072   :       90 0x5a 0132  Z      122 0x7a 0172  z
 27 0x1b 0033 ESC (escape)                      59 0x3b 0073   ;       91 0x5b 0133  [      123 0x7b 0173  (
 28 0x1c 0034 FS  (file separator)              60 0x3c 0074   <       92 0x5c 0134  \      124 0x7c 0174  |
 29 0x1d 0035 GS  (group separator)             61 0x3d 0075   =       93 0x5d 0135  ]      125 0x7d 0175  )
 30 0x1e 0036 RS  (record separator)            62 0x3e 0076   >       94 0x5e 0136  ^      126 0x7e 0176  ~
 31 0x1f 0037 US  (unit separator)              63 0x3f 0077   ?       95 0x5f 0137  _      127 0x7f 0177 DEL (delete)

Letters

The first four bits of any upper-case letter are 0100, while the first four bits of any lower-case letter are 0110.

To convert an upper-case letter to a lower-case letter, set the 3rd bit to 1, and to convert a lower-case letter to an upper-case letter, set the 3rd bit to 0.

Numbers

The first four bits of any number must be 0011.

To convert a number character to an integer data type, set the third and fourth bits to 0.