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The Timer is used to measure the time or generate an accurate time delay. It is an important application in an embedded system.

It maintains the timing of operation in sync with a system clock or an external clock.

How to use delay function of PIC Microcontroller part 7

The timer is used to count cycles and perform a particular action at a specified moment or optionally start an interrupt cycle. The digital cycles counted by the timer can be supplied internally through the peripheral clock or externally through a crystal, in this article we will look into the details of pic16fa timer with examples. Once it reaches the max value, it will roll back to zero setting up an Overflow flag and generates the interrupt if enabled.

Prescaler : Prescaler is a block that presents inside the timer module and it is used to divide the clock frequency by a constant. It allows the timer to be clocked at the rate a user desires. These timer module terminals are also multiplexed with other functions for handling alternate functions.

Timer 0 has a register called TMR0 Register, which is 8 bits of size. It is important to learn how time delay is calculated by the timer since the exact delay generation is the most common application of timer. Before filling this value timer registers should be configured as we shall see.

Timer 1 has a register called TMR1 register, which is 16 bits of size. Example: As the timer 2 is 8-bit and supports prescaler, it is not possible to directly generate the delay of 1 sec.

delay program for pic16f877a

The max delay with Prescaler will be:. Now us can be generated using timers which will be used to increment a counter times to get 1 sec delay.Counting and timing allows for controlling the brightness of LEDscontrolling the angle of servo shafts and PWM signal generation etc.

All microcontrollers have clocks in them or they use the one that resides outside of a microcontroller. Microcontroller needs clock so our programs can be executed in regularity with the clock. This is the basic function of microcontrollers. The PIC 18F is a high performance flash based microcontroller with 32 Kbytes of program memory and 1. Some special features of these Timers are given below:.

For Timer configurations, it is important to know that how time delay is calculated by the timer. Firstly the Timer clock source is set. The clock can be internal or external. In the internal clock mode Timer0 operates as timer and uses the internal F CPU clock with or without pre-scalar. When the Pre-scalar is set to one or bypassed then the timer runs on the same clock as the CPU is running. PIC 18F has ability for external as well as internal clock source but we are using Timer0 with internal clock Timer mode.

The values are reloaded again to start timer for same delay. Every Timer has certain registers associated, which must be configured for desired operations.

The Timer register can have the following bit length:. Timer0 Control Register:. The rising or falling transition of the incrementing edge for either input source is determined by the TMR0SE bitin the Control register. The prescaler is enabled by clearing the PSA bit of the Control register. There are eight prescaler options for the Timer0 module ranging from to The prescale values are selectable via the PS bits of the Control register.

In order to have a prescaler value for the Timer0 module, the prescaler must be disabled by setting the PSA bit of the Control register. This is Timer0 overflow flag bit which is bit is set when TMR0 register overflows.

This bit is cleared by the software. Both registers are separately accessible thus Timer0 can work in both 8-bit and bit modes. In these registers, pre-calculated value for delay is filled.

delay program for pic16f877a

Timer0 can operate as a timer or as a counter. When the clock source is the instruction cycle clock, it operates as a timer and when the clock source is the T0CKI pin, it operates as a counter.

This makes sure that the PIC18 always reads a bit value that its upper byteand lower byte belong to the same time. The time delay has been establishedhere by glowing a set of 8 LEDs one by one with a delay of 1 sec. The code is also given below.In this tutorial we are going to discuss the Timer module of Pic16fa.

First we will see what are timers, their working and later we will configure the PIC16fa timers to generate delay of ms and ms respectively. At the end we will see how to use the ExploreEmdedded Timer library. As the name suggests these are used to measure the time or generate the accurate time delay. Once it reaches the Max value, it will roll back to zero setting up an OverFlow flag and generates the interrupt if enabled.

Pic16fa has three indepenndent timer which can be used as timer,Counters or for PWM generation. Below table provides the details of the three Timers. PIC Oscillator frequency is divided by 4 and then fed to the controller, Now this this freq can be further divided by presacalar to generate the range of delays.

Time to increment the Timer count by one timer tick can be determined as below.

delay program for pic16f877a

Now the Timer value for the required delay can be calculated as below. Below is the sample code to blink the LEDs with 1ms delay. Delay measured using CRO:. Below is the sample code to blink the LEDs with ms delay. Generating 1sec delay using Timer2: As the timer2 is 8-bit and supports prescalar, it is not possible to directly generate the delay of 1sec. Now us can be generated using timers which will be used to increment a counter times to get 1sec delay.

Below is the sample code to blink the LEDs with 1sec us xtimes delay. Download the complete project folder from the below link: Hardware design Files and Code Library. Have a opinion, suggestionquestion or feedback about the article let it out here! Please enable JavaScript to view the comments powered by Disqus. Log in. PIC16fa Timer.

delay program for pic16f877a

This register holds the timer count value which will be incremented depending on prescalar configuration. This register holds the higher 8-bits of timer value. This register holds the lower 8-bits of timer value.We have just added one more button in LED board for this tutorial. Go through the tutorial to learn more. Timers are one of the important workhorses for an embedded programmer. Every application that we design will somehow involve a timing application, like turning ON or OFF something after a specified interval of time.

Because during the execution of Delay function the MCU sits dump by just creating a delay. Hence it is not advisable to use Delay functions except for applications like LED blinking where the Time delay need not be accurate or long. Physically, timer is a register whose value is continually increasing toand then it starts all over again: 0, 1, 2, 3, They are names as Timer0, Timer1 and Timer2.

In this tutorial we will be using the Timer 0 for our application. Once we understand the Timer 0 it will be easy to work on Timer 1 and Timer 2 as well. Now, let us see what each one really means. Prescaler is a name for the part of a microcontroller which divides oscillator clock before it will reach logic that increases timer status. For example if the value of prescaler is 64, then for every 64 th pulse the Timer will be incremented by 1.

As the timer increments and when it reaches to its maximum value ofit will trigger an interrupt and initialize itself to 0 back again. This interrupt is called as the Timer Interrupt. This interrupt informs the MCU that this particular time has lapped. The Fosc stands for Frequency of the Oscillatorit is the frequency of the Crystal used.

The time taken for the Timer register depends on the value of Prescaler and the value of the Fosc. In this tutorial we will set two buttons as two inputs and 8 LED as 8 outputs.

The first button will be used to set the time delay ms for every push and the second button will be used to start the timer sequence blinking. Check the Demonstration Video at the end of this Tutorial. Now, with these basics into mind let us look at our program given at the end in Code section. It is okay if you did not get the program, but if you did!! Give yourself a cookie and dump the program to enjoy your output. For others I will break the program into meaningful parts and explain you what is happening in each block.

As always the first few lines of the code are the Configuration settings and header files, I am not going to explain this since I have already did it in my previous tutorials. Next, let us skip all the lines and jump straight into the void main function, inside which we have the PORT configuration for the Timer0. Timer mode is selected by clearing bit 5 T0CS.

Now, the bits is used to set the prescaler value for the timer. As shown in the table above to set a prescaler value of 64, the bits must be set as The Timer will start incrementing once set and overflow after reaching a value ofto enable the Timer interrupt during this point the register TMR0IE has to be set high. This is same as that of our previous tutorial since we are using the same hardware. Except that we have added another button as input.Forums New posts Search forums.

PIC16F877A – Timer/Counter Tutorial

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Timers of PIC microcontroller How to generate delay

Forums Electronics Forums Microcontrollers. JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding. Thread starter Bob Parihar Start date Oct 28, Bob Parihar Member. Last edited: Oct 28, You're not clearing the timer1 interrupt flag. Whoops, yes you are but in a confusing way. Why PIR1. Otherwise, it looks correct. What is it doing besides "not working"? Edit, is your config right as you didn't include it.

And please, not a hex value. Pommie said:.

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Put in a bug report. As to the config, If you've stated RC oscillator and used a crystal then that will also stop it working. I'm just asking questions, just trying to help. You didn't answer my question, what is it doing beside not working! I'm now a bit drunk but trying to help.

Did I miss something? Still going crap if the above is correct.Remember Me? Re: 1 sec delay in pic16FA Code:. Re: 1 sec delay in pic16FA If you intend to use delay several times, will waste microcontroller processing. The best alternative is to use delay under interrupt conception. Re: 1 sec delay in pic16FA. If you intend to use delay several times, will waste microcontroller processing. If you use one of the hardware timers to generate periodic interrupts, you can create almost any delay you want and still run other tasks at the same time.

Looking at it from the opposite angle, if you use software loops to create delays and you also use interrupts for something else, every interrupt will make to delay longer than you want it to be.

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Originally Posted by betwixt. Re: 1 sec delay in pic16FA thank you evrybody. Re: 1 sec delay in pic16FA Hi If you use the code above in my earlier postyou should be able to get an idea of how the calculation works.

On a pic running at 4mHz, most instruction take 1 clock cycle to execute 1uS. There are a few that take 2, ie Call, Return and Goto are a few. If you download the data sheet for the pic, they contain the instruction set and the time taken to complete. Using the above details you can calculate how long each loop run will take to process, and then calculate the overall time to complete.

If you use this link Pic Delay Calculatoryou can play around with delay loops and look at the code produced to achieve the required delay. Hope that helps. Re: 1 sec delay in pic16FA visit compizspec. Originally Posted by chaudhryali Originally Posted by specospec. Re: 1 sec delay in pic16FA Some time ago I wrote a utility to help write assembler code for Pic16 series micros and posted it on eda board here. No install is needed, just extract all the files to a directory.

Call the directory PicHelp or whatever you like. Generates code for common constructs in programming. Please give it a go and see if it helps.

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Re: 1 sec delay in pic16FA thanks alot everyone. I think i can manage it now, cz of ur helps. Re: 1 sec delay in pic16FA One better approach is to avoid the uP to hang only in the delay routine and just to wait the ms period to expire.

The best solution is to use RTOS - in this case you can run several programs into a single uP I had in one of my projects with 16FA 6 inndent tasks simultaneosly running.

You'll be surprised how powerful becomes the uP when you use RTOS and also your productivity will jump because all programs become simpler and easier for maintanance.

Using PIC Timer with PIC16F84A

Once you start using RTOS you'll find out that even without RTOS you could create a program structure which makes possible many different tasks to executed in the same time. The main challenge is to convert the structure of the program in such way that it always passes through some common point you should not loop in single place or branch.

In this place you can put a check for the timer and if 1s expired ypu can execute something. The structure of the program should look like: Code:. Originally Posted by luben It's fully functional version without any limitations but has no sources only compiled libraries.If you read this tutorial, you could generate this precise delay for your applications.

As the name suggests these are used to measure the time or generate the accurate time delay. Now, let us see what each one really means. The main difference between them is that the bit Timer has much better Resolution that the 8-bit Timer. As the timer increments and when it reaches to its maximum value of for 8-bit timers or for bit timersit will trigger an interrupt and initialize itself to 0 back again. This interrupt is called as the Timer Interrupt.

This interrupt informs the MCU that this particular time has lapped. The time taken for the Timer register depends on the value of Prescaler and the value of the Fosc. The size of the register is 8 bits. Note: There is only one prescaler available which is mutually exclusively shared between the Timer0 module and the Watchdog Timer. A prescaler assignment for the Timer0 module means that there is no prescaler for the Watchdog Timer and vice versa. This is the 8-bit register which holds the timer values.

For example initially it will be 0. It will increment by one per one clock cycle. Then again starts from 0. That LEDs are blinking at every 1 second. Timer1 has a register called TMR1 register, which is 16 bits of size. Actually, the TMR1 consists of two 8-bits registers:. This flag marks the end of ONE cycle count.

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The flag need to be reset in the software if you want to do another cycle count. We can read the value of the register TMR1 and write into. We can reset its value at any given moment write or we can check if there is a certain numeric value that we need read. T0IF .