+------------+---------------------------------------------------------------+
| binary     |    0       1      2       3       4       5       6       7   |
+------+-----+---------------------------------------------------------------+
| 0000 |  0  |   NUL     DLE     SP      0       @       P       `       p   |
| 0001 |  1  |   SOH     DC1     !       1       A       Q       a       q   |
| 0010 |  2  |   STX     DC2     "       2       B       R       b       r   |
| 0011 |  3  |   ETX     DC3     #       3       C       S       c       s   |
| 0100 |  4  |   EOT     DC4     $       4       D       T       d       t   |
| 0101 |  5  |   ENQ     NAK     %       5       E       U       e       u   |
| 0110 |  6  |   ACK     SYN     &       6       F       V       f       v   |
| 0111 |  7  |   BEL     ETB     '       7       G       W       g       w   |
| 1000 |  8  |   BS      CAN     (       8       H       X       h       x   |
| 1001 |  9  |   HT      EM      )       9       I       Y       i       y   |
| 1010 |  A  |   LF      SUB     *       :       J       Z       j       z   |
| 1011 |  B  |   VT      ESC     +       ;       K       [       k       {   |
| 1100 |  C  |   FF      FS      ,       <       L       \       l       |   |
| 1101 |  D  |   CR      GS      -       =       M       ]       m       }   |
| 1110 |  E  |   SO      RS      .       >       N       ^       n       ~   |
| 1111 |  F  |   SI      US      /       ?       O       -       o      DEL  |
+------+-----+---------------------------------------------------------------+
  Hex code equals column/row position.  Control characters - change column 4
  codes to 0, column 5 codes to 1.  Combine 2 binary nybbles to make a byte.