Timer1 help

[jakeselectronics]

I've never used any timers and am about to try.

The idea:
Im using an LCD for a system, the details of the system are of no importance.

On power up I have the title of the system on the LCD.
after 2 seconds, I want to clear the screen.

I also have a keypad that I wish to scan.

Instead of writing characters to the display, execting a delay of 2 seconds, then clearing the screen; can i use a timer to interrupt the program and clear the screen.
this way i dont miss out on anytime scaning the keypad.


I am using a PIC16F72 which has Timer0 Timer 1 and Timer2.

With Timer1
If I set the Pre-Scaler to 1:8 does this mean the timer will increment every 8 cycles?
So its a 16bit timer, therefore it will count up to 65536.
For a for a delay of .5 seconds I will need to use 500,000 cycles (at 4MHz).
If I load the timer register with D'3036', It has to count 62500 cycles to reach 65536 for an overflow.
At a 1:8 pre-scaler (62500 x 8) I will get an overflow/interrupt every 500,000 cycles
which will give me an interurrpt every half second.

then I can count to 4 to get 2 seconds. or close to.

Am I On The Right Track?
Or Way Off??????

 

[Pommie]

It is normally better to interrupt at a higher frequency like 50Hz and count interrupts to make longer delays. A free running 50Hz interrupt can be easily achieved with Timer2 - PR2=125 postscaler=10 prescaler=16. Calling a routine to clear the screen from the interrupt is a bad idea as your main routine may be accessing the LCD. A better idea would be to do your keyscan on interrupt and the LCD in the main code.

Mike.

 

[jakeselectronics]

Calling a routine to clear the screen from the interrupt is a bad idea as your main routine may be accessing the LCD.

Good thinking.
I totally looked over that.

Alright I'll give the keypad interrupt a go.

Thanks again Mike.

 

[jbmillard]

I've done this recently...

I'm using a PIC24 (this is my first microcontroller project, so don't take this as gospel).

I have a main processing loop that checks for "flags" and does something when a flag is set, e.g. update display. The main processing loop is a never ending while loop. I set flags and do minimal processing from the interrupts. Some of my flags include display update, sleep commands, anything to do with peripherals, etc.

My button processing is done in a 1ms interrupt, it does the debounce and any menu routines that I have to update . These routines are very short/fast. These routines then set the "display flag" for the main processing routine.

I'm currently using three timers, one for a wait routine (it's separate because I need it enabled before the others), one at 1 second for longer delay items and one at 1ms for button processing. I keep counters to keep track of what needs to be done when. For example, my device sleeps after three minutes of no button presses. I increment a counter in the 1 second timer, when it reaches 180, I set the processing flag for the sleep command. When the interrupt exits, it goes back to the main processing routine which checks for that flag -- if set, it sleeps.

Brad

 

[jakeselectronics]

Sounds like a nice way of doing things jbmillard

Thanks for the ideas