Real Time Clock

[AvionicsMaster1]

Why won't DT interrupts work? I don't really understand all the code but it's fairly simple to plug in values to get any time base you'd like.

Just my 2 pennies here but I'd use at least 100 Hz and count pulses until you get to a second. From what I've read that further reduces timing errors by averaging the error over time.

Best regards

[m_flfl]

if you want very good accuracy you can use ds 1302 or ds1307 rtc time ic

[m_flfl]

but you can try this code


' 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