Clock

The following code only work with a 4 Mhz crystal, how can i get it to work with a 20Mhz crystal?

DEFINE OSC 20 does´t help, the clock ticks to fast whit a 20Mhz crystal

I use PicBasic Pro 2.50a

EDIT: I think i can change the number of "ticks" from 61 to something higher but how do i calculate the right value for the tick?

Code:

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' LCD clock program 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

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Add this into your program !!

Code:

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@ DEVICE PIC16F873,XT_OSC
@ DEVICE PIC16F873,HS_OSC               

DEFINE        OSC 20

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It's an example for a PIC16F873, if you have another chip than replace it.

Hi

Mister e has very kindly provided a calculator PICMultiCalc for just this sort of thing.

not quite sure how to provide link to a previous post on this forum, but a quick search should get you there


HTH

Duncan

This section...
' 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

...sets the interrupt frequency, based on a clock timer. When you change the clock speed, the interrupts still happen at the same number of clock cycles. The multicalc program that Mr. E has will help you calculate how often it is going now (documented at 16mS), and help you get there with the clock * 5.

Steve's Multi-Calc program is at;
http://www.mister-e.org/pages/utilitiespag.html
Just click on the download button and follow the directions. Then join the rest of us in saying 'Thanks Steve!'

Jerry.