Encoding  is  done  by  simply  loading  the  value  in  the  virtual  matrix  table  using  the
IREAD  instruction.  This  enables  us  to  easily  change   the   encoded   value   and   adapt   to
different keyboard layouts.                 After encoding, the interrupt routine will transition to fast scan state when the key is
released. This is to ensure that single key press will not be detected as multiple key strokes. Modifications and further options To accommodate a different 4 x 4 keyboard layout, it is very easy to just change the virtual matrix. The first entry  is  for  index  0  and  the  last  entry  is  for  the  index  value  of  0F (hex).                 Notice that all values are negated to enable display on LED on port B. A zero causes
the LED to be lit and an one will turn it off. If desired, the ~ sign can be removed to obtain
the true value. For example, the following matrix can be used for a 4 x 4 hexadecimal keyboard with real
value (not display value): virtual matrix   dw $F ; bottom right dw $E dw $D dw $C dw $B dw $A dw 9 dw 8 dw 7 dw 6 dw 5 dw 4 dw 3 dw 2 dw 1 dw 0 ; upper left Finally,  to  integrate  this  code  with  other  virtual  peripherals,  keep  in  mind  that  it  has  a varying execution rate depending on the state and therefore should be placed after code with
uniform execution rate.