| Timers, Clocks, RTC's: Elapsed Timer Demo | |||
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Elapsed Timer Demo Ticks var byte ' 1/100th of a second
Seconds var byte ' 0-59
Minutes var byte ' 0-59
Hours var byte ' 0-23
Days var word ' 0-65535
The time can be easily displayed with a single line: LCDout $FE,2, dec Days,"d-",dec2 Hours,":",dec2 Minutes,":",dec2 Seconds For each of the variables (Seconds, Minutes, Hours and Days) there is a flag that indicates when the value of that variable has changed. The Flags are: SecondsChanged var bit
MinutesChanged var bit
HoursChanged var bit
DaysChanged var bit
So, if you wanted to display the time like a clock, you could wait until SecondsChanged = 1, display the time, then reset the flag. Loop:
if SecondsChanged = 1 then
LCDout $FE,2, dec Days,"d-",dec2 Hours,":",dec2 Minutes,":",dec2 Seconds
SecondsChanged = 0
endif
Goto Loop
If you only wanted to display the time each minute instead of every second just do the same thing using the MinutesChanged flag. Loop:
if MinutesChanged = 1 then
LCDout $FE,2, dec Days,"d-",dec2 Hours,":",dec2 Minutes
MinutesChanged = 0
endif
Goto Loop
The timer can be Stopped and Started, like a stopwatch. Gosub StopTimer
Gosub StartTimer
The Elapsed.bas include file also Includes another file, ASM_INTS.bas This file can also be used in your other programs as well. It handles the "Context Saving" that is required for any Assembly language interrupt. It contains 2 macros: INT_START Saves the W, STATUS, PCLATH and FSR registers. This can be used at the beginning of your Interrupt routine. INT_RETURN Restores the W, STATUS, PCLATH and FSR registers after the Interrupt routine is finished and then returns from the Interrupt (RETFIE). Using it in a normal Assembly language interrupt might look something like this: Define INTHAND INT_CODE ' Tell PBP Where the code starts on an interrupt
ASM
INT_CODE
INT_START ' Save Context
... Your Interrupt routine goes here ...
INT_RETURN ' Restore Context
EndAsm
Using PBP statements in an ASM type interrupt Looking at the Elapsed.bas file, you'll see that even though the interrupt is being handled as an "ASM" type interrupt. The Handler is mostly PBP statements. A while back, Tim Box found out that it's possible to use PBP statements in assembly language interrupts, as long as you save any PBP system variables that may get overwritten by the interrupt routine. But instead of using up a lot of cycles saving variables that won't get overwritten, all you really need to do is save just the system vars that are actually used by the interrupt. In this case, the routine only uses R0 and R1. Finding out which system vars are used by the interrupt routine can be done a couple different ways. The first way is to compile the routine, and search thru the .LST file to see which system vars are used. This can be pretty difficult, especially since you have to follow any CALLS and look up their code in the PBPPIC14.LIB file. If your lucky, it won't take longer than several hours to find them all  Another way is to set each of the system variables to a known value at the start of the interrupt routine, then see if any of them have been changed after the routine is finished. It's probably a good idea to try it with several different starting values, just in case. Doing it this way is a little more risky. Unless all possibilities are tested in the interrupt routine, some of the system vars may not get changed during the test. They may come back to haunt you later on. I plan on making another post related to this topic. So if this doesn't make sense right now, Hang in there. Hopefully it will later. Well, I guess that covers most of it. if I've missed anything, or you still have questions, please don't hesitate to ask. |
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