Coundown timer on LCD

[chrisshortys]

Yes, unless you need really accurate timer, then the "add 1 to b1 and check value" sort of thing would be good enough for almost any project. I personally have only had timer experience with Mel's olympic timer and modified it somewhat to count either up or down, depending on another pin's level. I still haven't really nutted out the timer function or the interrupt bizzo, 'cos I figure I can simply use the modified Mel's timer for whatever I want. I don't think I really need to know EXACTLY why/how a PIC does what it does, I just need to know that it WILL do what it does. I have picked the timer and interrupt sections out of the original and simply use them when I need to. See?, plagerism is alive and well!!

Okay well after trying to get my head around this coding for several hours im going to have to ask for some help!
I ended up using the very very well written but advanced coding in the oylimpic timer. First of all i set up the programe running normally and checked that all options and modes etc were working fully.

I then started looking into making the programe count down instead of up so i set a value in the LCD display in the minutes and seconds incase it needed. (I dont know if there is a registry file which this info also needs to be placed into?)

I then looked at the coding and found the commands to change the seconds to 60 and minutes etc and change them to what i believe to be right:

' Timer Interrupt Handler
' =======================
TickCount:
Gosub SetTimer ' Set the Timer for next 10mS Interrupt
If RunningFlag=1 then ' If timing actually enabled... then...
Hundredths=Hundredths-1
' Increment 10mS Seconds Counter
If Hundredths<0 then
Hundredths=99
Seconds=Seconds-1
' Increment the Seconds
If Seconds<0 then
Seconds=59
Minutes=Minutes-1
' Increment the Minutes
If Minutes<0 then
Minutes=59
Hours=Hours-1
' Increment the Hours

If Hours>99 then
' Handle any Overflow
Hours=0
OverFlowError=1


Now im stuck. When i boot the programe up i get the time showing which ive set. I then start the timer and the tenth of seconds count down like i want them too! However it doesnt role over into the seconds.

Any help appreciated!

[skimask]

Now im stuck. When i boot the programe up i get the time showing which ive set. I then start the timer and the tenth of seconds count down like i want them too! However it doesnt role over into the seconds

Write a chunk of code that does this...
Take a byte variable, assign a value of ZERO to it, subtract one from that value and display it. For example:

temp var byte
temp = 0
temp = temp - 1
lcdout $fe , 1 , DEC temp

What's the result?
Is it what you expect?

[chrisshortys]

off the top of my head as im at work atm i would say that the result would remain zero as my old mentor told me that pbp doesnt do negative numbers?

Now thats where i believe the coding which reads:
If seconds <0 then
Seconds = 59 ?
Now that keeps the numbers rolling but i cannot see were the code which adjusts the next number sequence works.
I already have the hundredths of secs running downwards and everytime it reachs 0 it goes back to 99 i just dont see how to get it to affect the seconds.

[Kamikaze47]

as far as pbp is concerned, if temp is a byte variable and temp=0, then temp-1 = 255.