' Name        : CLOCKX.pbp
' Compiler    : PICBASIC PRO Compiler 2.6
' Assembler   : PM or MPASM
' Target PIC  : 40-pin 16F877A, 18F452 or similar
' Hardware    : Lab-X1
' Oscillator  : 4MHz external crystal
' Keywords    : ON INTERRUPT, IF THEN, LCDOUT, TIMER0
' Description : PICBASIC PRO program for an LCD clock using
' On Interrupt. Uses TMR0 and prescaler.  Watchdog Timer should be
' set to off at program time and Nap and Sleep should not be used.
' Buttons may be used to set hours and minutes.
'

Define LCD_DREG  PORTD   ' Define LCD connections
Define LCD_DBIT  4
Define LCD_RSREG PORTE
Define LCD_RSBIT 0
Define LCD_EREG  PORTE
Define LCD_EBIT  1

hour   Var Byte    ' Define hour variable
dhour  Var Byte    ' Define display hour variable
minute Var Byte    ' Define minute variable
second Var Byte    ' Define second variable
ticks  Var Byte    ' Define pieces of seconds variable
update Var Byte    ' Define variable to indicate update of LCD
i      Var Byte    ' Debounce loop variable

   ADCON1 = 7      ' PORTA and E digital
   Low PORTE.2     ' LCD R/W low = write
   Pause 100       ' Wait for LCD to startup

   hour = 0        ' Set initial time to 00:00:00
   minute = 0
   second = 0
   ticks = 0

   update = 1      ' Force first display

' Set TMR0 to interrupt every 16.384 milliseconds
   OPTION_REG = $55        ' Set TMR0 configuration and enable PORTB pullups
   INTCON = $a0            ' Enable TMR0 interrupts
   On Interrupt Goto tickint

' Main program loop - in this case, it only updates the LCD with the time
mainloop:
   PORTB = 0       ' PORTB lines low to read buttons
   TRISB = $f0     ' Enable all buttons

   ' Check any button pressed to set time
   If PORTB.7 = 0 Then decmin
   If PORTB.6 = 0 Then incmin  ' Last 2 buttons set minute
   If PORTB.5 = 0 Then dechr
   If PORTB.4 = 0 Then inchr   ' First 2 buttons set hour

   ' Check for time to update screen
chkup:
   If update = 1 Then
      Lcdout $fe, 1   ' Clear screen
 
      ' Display time as hh:mm:ss
      dhour = hour    ' Change hour 0 to 12
      If (hour // 12) = 0 Then
         dhour = dhour + 12
      Endif

      ' Check for AM or PM
      If hour < 12 Then
         Lcdout dec2 dhour, ":", dec2 minute, ":", dec2 second, " AM"
      Else
         Lcdout dec2 (dhour - 12), ":", dec2 minute, ":", dec2 second, " PM"
      Endif
      update = 0   ' Screen updated
   Endif

   Goto mainloop   ' Do it all forever

' Increment minutes
incmin:
   minute = minute + 1
   If minute >= 60 Then
      minute = 0
   Endif
   Goto debounce

' Increment hours
inchr:
   hour = hour + 1
   If hour >= 24 Then
      hour = 0
   Endif
   Goto debounce

' Decrement minutes
decmin:
   minute = minute - 1
   If minute >= 60 Then
      minute = 59
   Endif
   Goto debounce

' Decrement hours
dechr:
   hour = hour - 1
   If hour >= 24 Then
      hour = 23
   Endif

' Debounce and delay for 250ms
debounce:
   For i = 1 To 25
      Pause 10     ' 10ms at a time so no interrupts are lost
   Next i
   update = 1      ' Set to update screen
   Goto chkup


' Interrupt routine to handle each timer tick
Disable            ' Disable interrupts during interrupt handler

tickint:
   ticks = ticks + 1         ' Count pieces of seconds
   If ticks < 61 Then tiexit ' 61 ticks per second (16.384ms per tick)

' One second elasped - update time
   ticks = 0
   second = second + 1
   If second >= 60 Then
      second = 0
      minute = minute + 1
      If minute >= 60 Then
         minute = 0
         hour = hour + 1
         If hour >= 24 Then
            hour = 0
         Endif
      Endif
   Endif
   update = 1      ' Set to update LCD

tiexit: 
   INTCON.2 = 0    ' Reset timer interrupt flag
   Resume

   End