Working clock example using 32K watch crystal

[timc]

Looked all over trying to find an example with a second crystal connected to the TIMER1 overflow. This example uses the earlier 18F452 version of the Olimex PIC-WEB board. Ran the clock for a day without gaining or loosing a second! Lots of places where I was not sure what to do. Comments are welcome.
Regards
Tim C

' Name        : TMR1CLK.pbp
' Target PIC  : PIC18F452 or similar 18F types
' Hardware    : PIC-WEB ver A board with added LCD
' Oscillator  : 10MHz crystal. You May have to modify default 18F452 fuses for > 4Mhz
' Resolution  : Expect to get +- 5sec/day or better
' Description : PicBasic Pro program using external 32K watch xtal and Timer1
' interrupt for a real-time clock.
' Origional ver from: http://melabs.com/resources/samples/18f/tmr1clk18.htm  
'
DEFINE      OSC 10          ' We're using a 10MHz oscillator
DEFINE      LOADER_USED 1   ' Boot-Loader is being used
Define		INTHAND myint	' Define interrupt handler
Symbol		LED_0 = PORTD.5
symbol		BUTTON_0 = PORTB.0

wsave		VAR BYTE bankA system   ' Saves W
ssave		VAR BYTE bankA system   ' Saves STATUS

seconds		VAR BYTE bankA  ' variables within myint must be in bank 0.
minutes		VAR Byte      ' Elapsed minutes
hours		var byte

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

   ADCON1 = 7          ' Set PORTA and PORTE for digital operation
   Low PORTE.2         ' Enable the LCD

   Pause 150           ' Pause to allow LCD to initialize
   LCDOut $fe,1        ' Clear LCD

	hours = 2
	minutes = 23       ' Pre Set time here then add seconds to clock using button
	seconds = 0

	T1CON.7=0	' 8 Bit r/w (16 bit seems to cause problems)
	T1CON.5=0	' Part 1 of 1:1 prescale
	T1CON.4=0	' Part 2 pf 1:1 prescale
	T1CON.3=1	' turn on the low freq clock osc
	T1CON.2=1	' Do not Sync low Freq clock with main clock
	T1CON.1=1	' use 32Khz xtal as the Timer1 source
	T1CON.0=1	' enable Timer1
		
	PIE1 = $01         ' Enable TMR1 overflow interrupt
	INTCON  = $C0      ' Finally Enable global interrupt and peripheral interrupts

   GoTo mainloop          ' jump over the interrupt handler and sub

   ' Assembly language interrupt handler
Asm
myint
   ; Save the state of critical registers
   movwf   wsave      ; Save W
   swapf   STATUS, W  ; Swap STATUS to W (swap avoids changing STATUS)
   clrf    STATUS     ; Clear STATUS
   movwf   ssave      ; Save swapped STATUS

   ; Set the high register of Timer1 to cause an interrupt every
   ; 32768 counts (2^15).

   movlw   080h       ; Prepare to set TMR1 high register
   movwf   TMR1H      ; Set TMR1H to 80h
   incf    _seconds,F ; INCREMENT seconds COUNT
   bcf     PIR1, 0    ; Clear interrupt flag

   swapf   ssave, W   ; Retrieve the swapped STATUS value (swap to avoid changing STATUS)
   movwf   STATUS     ; Restore it to STATUS
   swapf   wsave, F   ; Swap the stored W value
   swapf   wsave, W   ; Restore it to W (swap to avoid changing STATUS)
   retfie             ; Return from interrupt
EndAsm

' Subroutine to update the time variables
get_time:

	if seconds > 59 then
		seconds = seconds - 60	' better then making seconds=0
		minutes = minutes + 1
		if minutes > 59 then
			minutes = 0
			hours = hours + 1
			if hours > 12 then	' simple 12 hour clock format
				hours = 1
			endif
		endif
	endif      

Return

mainloop:

	GoSub get_time      ' Update minutes and seconds
	TOGGLE LED_0

	LCDOut $fe,2,"Time: ",DEC hours, ":", DEC2 minutes, ":", DEC2 seconds, "   "

	Pause 300           ' Pause to see LED blink. Also help with debounce
	if button_0 = 0 then
		LCDOut $fe,$C0,"+1s "
		seconds = seconds + 1
		else
		LCDOut $fe,$C0,"     "
	endif
	GoTo mainloop       ' Repeat main loop

   End

[malc-c]

' Description : PicBasic Pro program using external 32K watch xtal and Timer1

But 50% of the program is in assembler

[Darrel Taylor]

But 50% of the program is in assembler

Then show him how it's done. (in straight PBP)
This task is worth 2 free 4x20 Parallel LCD's ... shipping outide of US/Canada extra.

In case of multiple responses ... style will prevail.
As judged by Darrel Taylor
Ends 11/10/2010 Midnight Mountain Time

[Archangel]

INCLUDE "DT_INTS-18.pbp" ; Base Interrupt System
INCLUDE "ReEnterPBP-18.pbp" ; Include if using PBP interrupts"

[timc]

The earlier versions I wrote had NO asm but lost almost a minute an hour. To make up for that one could re-tune using TMR1H and TMR1L with a larger value. Problem is every change made to the program would mean spending a few days retuning and it would never be as precise.

So yea I would love to be able to do this without asm in PBP AND be as accurate!

Down the road I intend to join this interrupt sample with a SNTP internet program so I can have a near perfect millisecond low power $60 clock.

Regards
Tim C

[Bruce]

   ' Int handler doesn't mess with any PBP system variables - or lower 15-bits
   ' of TMR1 accumulated time. Uses only 4 instructions to set TMR1H high bit,
   ' increment seconds, clear the interrupt flag bit, save & restore WREG, STATUS,
   ' BSR and return from int handler.
 
@myint                  ; create myint label
   TMR1H.7=1            ' Set TMR1 high bit for 1 second overflows
   seconds = seconds+1  ' Increment seconds
   PIR1.0=0             ' Clear TMR1 int flag
   @ retfie  FAST       ; Return with 'auto restore' of WREG, STATUS and BSR

Should do it.

[malc-c]

Then show him how it's done. (in straight PBP)

I wish --- (I'll remove my tongue from in my cheek now )

[timc]

Thank you Bruce
Smaller, tighter, yet perfect speed. Started the clock last night with your change and so far the PIC18F452 has not gained or lost one second.
Tim C

[Acetronics2]

Hi,

I didn't see that one :
http://www.pbpgroup.com/modules/wfse...hp?articleid=8

did I miss something ???

Alain