' Name        : TMR1CLKX.pbp
' Compiler    : PICBASIC PRO Compiler 2.6
' Assembler   : PM or MPASM
' Target PIC  : 40-pin 16F877 or similar
' Hardware    : LAB-X1 Experimenter Board
' Oscillator  : 4MHz external crystal
' Keywords    : ASSEMBLY INTERRUPTS, LCDOUT, TIMER1
' Description : PICBASIC PRO program that demonstrates the use of
' Timer1 interrupt for a real-time clock. Written for the LAB-X1
' experimenter board with a 16F877.
'

' Define LOADER_USED to allow use of the boot loader.
' This will not affect normal program operation.
Define LOADER_USED 1

' Define interrupt handler
Define INTHAND myint

wsave  VAR BYTE $20   system
wsave1 VAR BYTE $a0   system  ' Necessary for devices with RAM in bank1
wsave2 VAR BYTE $120  system  ' Necessary for devices with RAM in bank2
wsave3 VAR BYTE $1a0  system  ' Necessary for devices with RAM in bank3
ssave  VAR BYTE bank0 system
psave  VAR BYTE bank0 system

TICK   VAR BYTE bank0	' make sure that the variables are in bank 0
                        ' if they are to be used in the interrupt handler

seconds VAR BYTE        ' Elapsed seconds
minutes VAR WORD	' Elapsed minutes
	
   minutes = 0		' Clear time
   seconds = 0

   T1CON = $01		' Turn on Timer1, prescaler = 1
   INTCON 	= $C0	' Enable global interrupts, peripheral interrupts
   PIE1 = $01		' Enable TMR1 overflow interrupt

   GoTo main	        ' jump over the interrupt handler and sub
 
' Assembly language interrupt handler
Asm
myint 
; Uncomment the following if the device has less than 2k of code space
   ;movwf  wsave	 ; Save W
   ;swapf  STATUS,W	 ; Swap STATUS to W (swap avoids changing STATUS)
   ;clrf   STATUS	 ; Clear STATUS
   ;movwf  ssave	 ; Save swapped STATUS
   ;movf   PCLATH,W	 ; Move PCLATH to W
   ;movwf  psave	 ; Save PCLATH

; Set the high register of Timer1 to cause an interrupt every
; 16384 counts (65536-16384=49152 or $C000). At 4MHz, prescale
; set to 1, this equates to a tick every 16384uS.  This works
; out to about 61 ticks per second, with a slight error.  The
; error could be reduced substantially by setting the TMR1L
; register and playing with different values for the prescaler
; and the ticks per second.

   movlw  0C0h		; Prepare to set TMR1 high register
   movwf  TMR1H		; Set TMR1H to C0h
   incf   _TICK,F	; INCREMENT TICK COUNT
   bcf    PIR1,0	; Clear interrupt flag

   movf   psave,W	; restore the state of everything
   movwf  PCLATH
   swapf  ssave,W
   movwf  STATUS
   swapf  wsave,F
   swapf  wsave,W
   retfie   		; Return from interrupt
EndAsm

' PicBasic subroutine to update the minutes and seconds variables
get_time:
   ' Update the time when needed. The TICK variable will
   ' overflow if you don't update within 4 seconds.  This could
   ' be done in the interrupt handler, but it's easier to do
   ' it in PicBasic, and you usually want the interrupt handler
   ' to be as short and fast as possible.
 	
   PIE1 = 0			 ' Mask the interrupt while we're messing with TICK
   seconds = seconds + (tick/61) ' Add the accumulated seconds
   tick = tick // 61		 ' Retain the left-over ticks
   PIE1 = $01			 ' Interrupt on again
   minutes = minutes + (seconds / 60) ' Add the accumulated minutes
   seconds = seconds // 60	 ' Retain the left-over seconds
   Return			 ' Return to the main program

main	
   ' Begin program code here.  The minutes and seconds variables can
   ' be used in your code.  The time will be updated when you call the
   ' get_time routine. Disable interrupts while executing timing-critical
   ' commands, like serial communications.

DEFINE LCD_DREG  PORTD
DEFINE LCD_DBIT  4
DEFINE LCD_RSREG PORTE
DEFINE LCD_RSBIT 0
DEFINE LCD_EREG  PORTE
DEFINE LCD_EBIT  1

loops VAR WORD
loops = 0

   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

mainloop:
   loops = loops + 1
   LCDOut $fe,$C0,"Loops Counted: ", DEC5 loops
   GoSub get_time	' Update minutes and seconds
   LCDOut $fe, 2, "Time: ",DEC5 minutes, ":", DEC2 seconds ' Display the elapsed time
   GoTo mainloop 	' Repeat main loop
	
   End