Hi all,

I have a low RPM motor which is connected to a sensor which outputs a pulse with every rotation. Now I want to connect this sensor with the 8051 counter. I will also be using a momentary switch which when pressed will short to ground.
Now I want the counter to only operate when the switch is pressed (ex: if the switch is pressed for 5seconds, the counter will only count the rotations for that period). When the switch is released I need to read the counts to determine the rotations at that period and reset the counter for the next button press.
A timer of 2 seconds will also be enables with the switch release.

I other words, I need a counter and a timer. I was planning to use Timer 0 in Mode 1 as the counter and Timer 1 in mode 0 for the 2 seconds delay.

Which is the best mode to use for this combination?
Is is possible to achieve a 2seconds delay in Mode 0 using the prescaler?

Any help would be highly appreciated.

 

I'm not sure you can get all the way to 2 seconds with just a hardware timer. If so you can go with whatever works.
If not then the most convenient thing you can do is to set the timer up so it auto-reloads when it expires so the time between the interrupts is always constant. Then no matter how long it takes to process the interrupt, every 'tick' will be the same length. Count interrupts until 2 seconds has passed and set a flag in the interrupt routine that you can check and reset in the non interrupt code. DONT make the mistake of coding the process to be invoked every 2 seconds into the interrupt routine. That is the road to perdition.

 

Hi again,
Can I use timer 1 if timer 0 is used in mode 3?
I was looking at the datasheet and realized that in mode 3, both TF0 and TF1 are used. So I assume that that if one timer is in this mode, the other timer cannot be used.

 

Basically I want to use two timers and one counter. Now I need to use the overflow interrupt of timer 0 and one overflow interrupt of timer 1 (since I cannot use three overflow interrupts). Is this possible to do this when used the timers in the modes shown in the attached diagram?

Any help would be highly appreciated.

 

I don't think so, but if you give me a link to specific datasheet I might be able to come up with something.

 

Thanks for the reply. I am using the T89C51AC2. Datasheet: http://www.atmel.com/images/doc4127.pdf

 

Timer 1 in mode 3 just halts and doesn't do anything.

Placing Timer 1 in mode 3 causes it to halt and hold its count. This can be used to halt
Timer 1 when TR1 run control bit is not available i.e. when Timer 0 is in mode 3.​

I don't think it will work the way you want it to. Is timer 2 also in use?

 

For timer interrupts, I would suggest you to read how to use Timer interrupt in 8051 Microcontroller, as they have explained in detail. They have also given the code and Proteus Simulation which you can download from this link. I hope it will help.

 

It is fairly easy.

1 set up your timer to trip periodically. Let's say once every 10ms.
2 in the timer isr, count the number of times the isr has been called. Count up or count down, it doesn't matter.
3 once the timer isr has been called the desired number of times, 200 in this case, reset the counter and do your task,, or set a flag to do your task.

This is a fairly standard approach.