' =========================================================================
'
'   File....... Encoder.BS2
'   Purpose....
'   Author..... Jon Williams -- Parallax, Inc.
'   E-mail..... jwilliams@parallax.com
'   Started....
'   Updated.... 13 DEC 2004
'
'   {$STAMP BS2pe}
'   {$PBASIC 2.5}
'
' =========================================================================


' -----[ Program Description ]---------------------------------------------


' -----[ Revision History ]------------------------------------------------


' -----[ I/O Definitions ]-------------------------------------------------

EncPort         VAR     INA


' -----[ Constants ]-------------------------------------------------------

Span            CON     100                     ' set value 0 - 99

NumTasks        CON     3


' -----[ Variables ]-------------------------------------------------------

encNew          VAR     Nib                     ' current scan
encOld          VAR     Nib                     ' old scan
value           VAR     Byte
task            VAR     Nib


' -----[ EEPROM Data ]-----------------------------------------------------


' -----[ Initialization ]--------------------------------------------------

Reset:
  encNew = EncPort >> 1 & %0011                 ' read current inputs
  encOld = encNew


' -----[ Program Code ]----------------------------------------------------

Main:
  DO
    GOSUB Check_Encoder
    ON task GOSUB Task_0, Task_1, Task_2
  LOOP

  END


' -----[ Subroutines ]-----------------------------------------------------

Check_Encoder:
  encNew = EncPort >> 1 & %0011                 ' read current inputs
  IF ((encNew ^ encOld) <> 0) THEN              ' test for change
    IF (encOld.BIT0 ^ encNew.BIT1) THEN         ' test direction
      value = value + 1 // Span                 ' increment value
    ELSE
      value = value + (Span - 1) // Span        ' decrement value
    ENDIF
    encOld = encNew                             ' save current inputs
  ENDIF
  RETURN


Task_0:
  DEBUG HOME, DEC value, CLREOL                 ' print value
  task = task + 1 // NumTasks                   ' update task pointer
  RETURN


Task_1:
  ' do something
  task = task + 1 // NumTasks
  RETURN


Task_2:
  ' do something
  task = task + 1 // NumTasks
  RETURN 