Timer in real time

hello,

One of my friend ask me to post the question here:

Marc, My friend, want to know how he can make a timer in real time (24 hours/day) to make a specific task.

In the bottom I have paste his example code that he want to start with. Marc want to know which specific crystal and prescaler are required? and if this method is good to get a second, minutes and hours equal to a real to the real world time.

Let us know if you are a better ways to get the result.

Thanks!
Martin and Marc!



He want to make his program starting with this code example, here is the 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 PORTb ' Define LCD connections
Define LCD_DBIT 4
Define LCD_RSREG PORTb
Define LCD_RSBIT 3
Define LCD_EREG PORTb
Define LCD_EBIT 0
define LCD_BIT 4
DEFINE LCD_LINES 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


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 1:64 16.384 milliseconds
OPTION_REG = $15 ' Set TMR0 configuration and 1:64
INTCON = $a0 ' Enable TMR0 interrupts
On Interrupt Goto tickint


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

' Check any button pressed to set time
If PORTA.0 = 1 Then decmin
If PORTA.1 = 1 Then incmin ' Last 2 buttons set minute
If PORTA.2 = 1 Then dechr
If PORTA.3 = 1 Then inchr ' First 2 buttons set hour

' Check for time to update screen
chkup: If update = 1 Then
Lcdout $fe, 1 ' Clear screen ,l

' 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

Salut Martin

There's a simple way to do it, but require a bit of extra hardware. An RTC, something Like DS1307. Really easy to use. That way, no need to care about the timing and blah blah blah. Just read the RTC when you want and do the according stuff.

I would recommend the use of an RTC

(DS1307 or similar.)
Search the forum for RTC*
and you'll find many examples.

EDIT: Steve, you have won (as usual)

Hello,

thanks for your reply. my friend has already analyzed the RTC solution. He wants something software that is included in a PIC also for further development, very low cost and very simple.

anything else ?

Do a search for the Olympic Timer thread...

There's a bunch of other idea that spring to mind. Is the unit will be battery powered or AC powered?

If it's AC powered, i would prefer to use the AC as timebase, use an internal timer interrupt to get the 1 Second or 1 minute. Once in the interrupt do the math and check for Alarm or Events.

BUT you can do it with the internal Tick FOSC/4, in this case use one of the lower Crystal frequency... let's say 4 MHZ => internal = 1MHZ => ticks every 1 uSec => internal timer interrupt every 1000 counts to have a time base of 1 Sec => you need a 16 bits Timer.

Wich PIC Marc will use ???

Process is almost the same than with an RTC but you'll have to deal with a bunch of more code line to take care of the days of week/month/year/Leap Year/hours/minutes... BLAH BLAH BLAH, tsé veux dire !!!

NOT impossible, a bit tricky, i agree.

What the unit will also do?

HEllo

Marc make an automatic food system for Deer hunting. It's a little contract that ones of his neighboor ask for.

Marc use a 16F84A-4MHz. Unit will be DC powered.

He will get back to me soon. He actualy looking at some tricks mentionned here.

I Will let you know how is going with his tests.

thanks again!

Martin et Marc

Martin & Marc,

I just posted in the “Code Examples” area two examples of how to create easy clocks that track time in an HH:MM format. The examples do not require Real Time Clock (RTC) ICs and are based on 4MHz Crystals. They are highly accurate at < 2 sec /day error with a standard 4.000MHz crystal (with +/- 20ppm tolerance.)

Both examples use TMRO with prescalers set to 256. This method requires only about 30 lines of code to maintain accurate time.

The programs are named EZClock1.bas and EZClock2.bas. These files are mostly comment - the code is at the end.

Maybe these can help your friend -

Good Luck,
Paul Borgmeier
Salt Lake City, Utah
www.cruxanalysis.com