PIC Timers and Counters (Part 1) | Anna university questions papers projects for EEE,ECE,IT,MECHANICAL,MBA,MCA Anna university questions papers projects for EEE,ECE,IT,MECHANICAL,MBA,MCA: PIC Timers and Counters (Part 1) Bank Exam question paper, GATE Papers,Combined Defence Service Examination papers ,TANCET,BSNL JTO,ISRO,EBOOKS,DRDO ,BARC, , NTPC ,BHEL ,BEL ,HAL,Anna University Papers,ECE , EEE , CSE , IT , Mech , BIOMEDICAL , Textile , MBA , MCA , Anna University Question Bank , Anna University Syllabus , Anna University 'Q' Papers , Gate Papers , 8051, AVR, 8051 projects, free 8051 microcontroller projects, AVR projects, AVR tutorial, AVR microcontroller projects, circuits, hobby electronics, microcontroller based projects, microcontroller projects, final year projects, electronic projects, electronics projects, circuit diagrams, pin diagram, pin description, interfacing with AT89C51, 8051 tutorials, embedded projects, serial port, sensor, Electronic Components, Electronic Circuits, circuits for hobbyist, electronic schematics, DIY projects, breadboard circuits, at89c51, 8051 code, advanced circuits, hobby projects, circuit ideas, embedded system, embedded C, microcontroller programming in C, LCD interfacing, ADC interfacing, circuit components, hobby circuits, seven segment display, 89c51 projects, circuit description, major projects, minor projects, projects for circuit branches, interrupt, 8051 programming, RS232, 8 bit microcontroller,Microcontroller Tutorials, PIC Tutorial, 8051 Microcontroller Tutorial Resource, Connect to the PIC, PIC Tutorials, Micro Controller Tutorials, PIC Micro controller Tutorial Resource, DALLAS 80C320, DS80C320, Connect to the PIC, PIC Tutorials, Dallas DS80C320, 8051 Introduction, Types of Memory, Special Function Registers, Basic Registers, Addressing Modes, Program Flow, Low Level Information, 8051 Timers, 8051 Serial Port Operations, 8051 Interrupts, Additional Features of 8052, 8052 Instruction Set, Computer Science Seminar Topics, Mechanical Engineering Seminar Topics,Electrical Seminar Topics,Electronics Seminar Topics,Seminar Abstract And Report Downloads,High-Speed Architecture, New Instruction Speed, Variable Length MOVX Instruction, Timer Considerations, Dual Data Pointer, Watchdog Kicking, The Watchdog Watchdog Interrupt, Watchdog System Resets, Power Failure Functions, Power Failure Reset, Power Failure Interrupt, Secondary Serial Port, Timed Access Protection, PIC16F877A Tutorial, Introduction to the PIC16F877A, How to hook up the PIC so it will run?, What do the pins mean?, How to program the PIC?, Miscellaneous Advice, LED Blinker, Photoresistor Input, Analog Input (Photoresistor, Sonar sensor, IR sensor, Digital Input (Switches), Output messages to computer screen, Servo Motor Output, DC Motor Output,Gate sample paper with solution , Engineering E-Books , Free ebook websites , Final Year Projects , Placement papers,anna university previous year question bank, previous year question paper,model question paper, two mark question paper,sex,adult,results,atmel humidity Assembly Language code, Digital Clock Employing Memory Mapping, Humidity Sensing, Microcontroller51,control solid state relays, decoded 74ls138, latech 73ls373, port expander, Solid State Relays,urn ON, turn OFF, Relay Driver, back EMF, holding, current, pullup, resistor, coil, BC547, ULN2003, ULN2803, npn, transistor, microcontroller, Technology, circuit,bharathidasan university,university,thanjavur,madurai,coimbatore,chennai,adult,porn,sastra,sastra university, placement and training cell,java,j2ee,ajax,c,c++,oracle,COMPUTER SCIENCE,embedded, embedded systems, j2ee, dotnet, j2me, dot net, jsp, vb, c#, c, c sharp, computer science, cse, information technology, it, Electrical, Electronics, communication,SURVEY,ONLINE JOB,PAY TO CLICK,SEBOSA, ece, eee, academic, college, instrumentation, control, control systems, best ,project centers, project centres, company, companies, software, telecommunication, telecom, networking, matlab, robotics, Artificial intelligence, automation, cloud computing, cryptography, data mining, dsp, database, digital, image processing, fuzzy logic, gsm, gps, gprs, mobile computing, networks, network security, php, power, systems, vlsi, hardware, web services, wireless, rf, rfid, microcontroller, ns2, 2010, titles, list, download, latest, free, advanced, low cost, placement, zigbee, Chennai, india, uk, SOFTWARE ENGINEERING, APPLIED ELECTRONICS, VLSI Design, M.E,EMBEDDED SYSTEMS, COMMUNICATION SYSTEMS,Memory Organization, Microcontroller to LCD, moving message display using 8051 microcontroller, MOVING MESSAGE DISPLAY USING ATMEL 89C51, PIN Configuration, Programming Aspects, POWER ELECTRONICS, 89c51, 89s51 moving message display board, microcontroller 8051,8051, AVR, 8051 projects, 8051 microcontroller projects, AVR projects, AVR tutorial, AVR microcontroller projects, electronics projects, free electronic circuits, circuit diagrams, circuits, schematics, hobby electronic projects, electronic projects, hobby electronic circuit diagram, final year projects, embedded projects, technical articles. Interfacing microcontroller 8051 with peripherals like ADC, LCD, EEPROM,solenoid valve atmel dc control triac,dimmer bt138,uln2003 microcontroleur interfacing a microprocessor to a power thyristor microcontrol based level mesurement 89c51 as pwm controller,at89c2051 sine wave pwm,8051 lift, circuit design for a elevator, Elevator Lift control for three stories with microcontroller 8051, microcontroller based lift controller for three stories, three stories lift,ericsson at command microcontroller, GSM/ EDGE Modem in PCI Interface, Interface of mobile phone with micro-controller, Supporting AT commands,embedded projects,8051,pic,arm,pic16f877a,qualifity,best project in thanjavur,relay design,product manufuring,dvd,vcd,service,free training,electrical and electronic circuits,pcb board design,help of embedded,earn money with embedded,part time job,home based job,vacancy,ieee transaction,optimization,website design,university, Chapter 2 Liquid Crystal Display, Character Generator RAM, DDRAM or CGRAM, Display on or off control, LCD, microcontroller interface with LCD, PIN Configuration, Pressure monitoring with microcontroller 8051, Pressure sensing and controlling, Pressure Sensing System, Programmable Peripheral Interface, RS-232 serial communication,diploma in embedded,matlab in thanjavur, seo,site design @2900 onwards, 8255 and RS232, 89s51 LCD display LM 35 ADC0804 measurment, construction of a pressure sensing system using 8051, designed pressure sensor and transducer,microcontroller based heart rate meter,8051 pin diagram,invention heart rate meter,heart meter watch,heart beat monitor project,8051,AVR,8051 projects,free 8051 microcontroller projects,AVR projects,AVR tutorial,AVR microcontroller projects,circuits,hobby electronics,microcontroller based projects,microcontroller projects,final year projects,electronic projects,electronics projects,circuit diagrams,pin diagram,pin description,interfacing with AT89C51,8051 tutorials,embedded projects,serial port,sensor,Electronic Components,Electronic Circuits,circuits for hobbyist,electronic schematics,DIY projects,breadboard circuits,at89c51,8051 code,advanced circuits,hobby projects,circuit ideas,embedded system,embedded C,microcontroller programming in C,LCD interfacing,ADC interfacing,circuit components,hobby circuits,seven segment display,89c51 projects,circuit description,major projects,minor projects,projects for circuit branches,interrupt,8051 programming,RS232,8 bit microcontroller,microcontroller based heart beat monitor,8051 isp programmer,heartbeat monitor and display on LCD,heart beat rate monitor with sensor,training heart rate monitor with comaprators ans sensor,8051 microcontroller application,optocoupler based sensor of runner heart rate monitor,how to measure heart beat, calculate heartbeat just in one second,8051 rtos,limitations of heart rate monitors, quick display of heart monitor,advantages of electronic medical records,electronic medical billing,used electronic test equipment,electronic document management solution,fetal heart rate monitor,wrist heart rate monitor,avr 8051,baby heart monitor,heart beat counter using microcontroller 8051, block diagram for ir led and ldr based heartbeat monitor with display on computer, MICROCONTROLLER AT89C2051 BASED HEART BEAT MONITOR (PULSE RATE wth assembly code),ir led and ldr based heartbeat monitor with display on computer,wireless biomedical monitoring system using 89S52 microcontroller,wireless biomedical monitoring system using 89S52 microcontroller,8051microcontroller based heart beat monitor,heart pulse system project,very cheap cost in india,lm35,temperature sensor,heart beat sensor,technology,solutions,sastra university,data base design,speed ,innovative centre,home security system model design, water level indicator for home,COMPUTER SCIENCE, SOFTWARE ENGINEERING, APPLIED ELECTRONICS, VLSI Design,IEEE Project center, IEEE 2010 Projects in Tanjore, trichy, Kumbakonam, Pudukkottai, Ariyalur, Pattukkottai, Best IEEE Projects, final year projects, Project Center in Trichy, Project Company in thanjavur, Project training @ tanjore, Free 8051 Microcontroller projects,8052 projects,microcontroller,projects, Datasheers,circuit diagram,Microcontroller,8051,AVR,8085 Microprocessor,BASCOM,projects,tutorials,codes,Libraries,interfacing examples,embedded projects,serial port,infrared remote controls,rf remote controls,home automation,Intel 8051 microcontroller,electronic projects,embedded systems,control systems,computers,technical books,software,assembly language,programming intels 8051,serial communications,rs232,Electronics Projects,Books,Home Automation,Computer Software,Assemblers,Compilers,applications Programming,Embedded Systems Design,8052,AT89C2051,robotics applications,visualbasic, Microsoft Visual Basic,system, based, solar, control, intelligent, motor, controller, vehicle, monitoring, pwm, detection, home, temperature, tracking, alert, blind, alcohol, automated, automatic, close,Robotics,Kits,Circuit Examples,8051,Robots,micro Code,AT89c51, Programmer,IEEE 2010 embedded systems, embedded programming, PIC Micro projects, Microchip Programming, AVR tutorials, PIC Micro tutorials, ATMEL, Microcontrollers based systems, Microcontroller Projects, Embedded projects, Embedded designing in C, Microchip Lab, Embedded systems tips, DIY Electronics,Project Detail,onlinejob, Data Entry, no fee, no investment, part time, home based,recuirements,job,consultancy,helpline,maths,power,ultimate knowledge,prodigy,trichy,mobile
100% FAT LOSS TIPS Click Here!

PIC Timers and Counters (Part 1)

, Posted by ADMIN at 11:10 AM

Description

PIC microcontrollers are equipped with one or more precision timing systems known as Timers. They can be used to perform a variety of time precision functions, such as generating events at specific times, measuring the duration of an event, keeping date and time record, counting events, etc. The main component of a timer module is a free running binary counter that increments for each incoming pulse. Since it runs independently, it can count pulses concurrently with the main program execution. A PIC16F688 microcontroller has two built-in hardware timer modules: Timer0 and Timer1. Today's lab lesson will explore the functionality of the Timer0 module.

Required Theory

The fundamental concept of a timer/counter module is discussed in Timers and Counters. It is simply an independent binary counter that can be configured to count instruction cycles or to count external clock pulses. The Timer0 module in a PIC16F688 microcontroller is an 8-bit synchronous counter that stores the value for the counter in the special function register called TMR0. This register can be read or written at any time by software. If you write a value to it, the counter will start incrementing from there.

When the Timer0 module is driven by the processor's instruction clock, it is said to operate as a timer because it increments at a constant rate (defined by the processor clock) and if you know the number of pulses counted, you can derive how much time has elapsed. The Timer0 can also count external pulses arriving at the RA2 pin (11), which has the alternate name T0CKI (Timer Zero Clock Input). While counting the external pulses, it is said that it operates as a counter. We will discuss the two modes of Timer0 separately.

Block diagram of Timer0 Module (Source: Microchip)

Timer mode

Timer mode is selected by clearing the TOCS bit (OPTION register, bit 5). In timer mode, the TMR0 register increments every instruction cycle. As an 8-bit register, TMR0 can count from 00 to FF (255). When it reaches its maximum value, FF, and is incremented further, it rolls over to 00. This register overflow is recorded by the T0IF (Timer0 Interrupt Flag) bit of the INTCON (Interrupt Control) register by being set to 1. The T0IF bit set can trigger an interrupt (known as Timer0 Interrupt), if enabled. [An interrupt is an asynchronous signal calling for processor attention. It tells the microcontroller to drop whatever it's doing and go to a predefined place (the interrupt service routine or ISR) when a certain event occurs. We will discuss it more in upcoming lab sessions]. The Timer0 interrupt is enabled by setting the T0IE bit (Timer0 Interrupt Enable) of the INTCON register along with the Global Interrupt Enable (GIE) bit. This interrupt would be the indication of the time out and will occur on the every overflow of the TMR0 register. The TOIF bit must be cleared by the interrupt service routine so that the timer interrupt can take place again.

Suppose, if you are running a PIC with a 4 MHz clock, the instruction clock will be 1 MHz (1 instruction cycle = 4 clock cycles, for PIC). The counter would then be clocked every 1 μs exactly. That means, the Timer0 will take 256 μs to count from 0 to 0. By preloading the TMR0 register with a suitable value, a smaller timer interval could be selected, with time out indicated by the timer interrupt. For example, if you preload the TMR0 register with the value 206, the Timer0 overflow would occur after 50 μs.

Besides, an eight bit programmable divider, known as prescaler, is also available to measure a longer time period. The prescaler is a dividing circuit between the clock source and the timer, and it divides the input frequency by one of eight binary values between 2 and 256. With 1 MHz instruction clock, the maximum timer period would be 256 x 256 μs = 65.536 ms, corresponding to the prescaler value of 256. The prescaler values are software selectable through PS0, PS1, and PS2 bits of the OPTION register. In order to use the prescaler with the Timer0 module, the PSA (Prescaler Assignment) bit of the OPTION register must be cleared. If the PSA bit is set, no prescaler will be assigned to the Timer0 module. The individual bits of the OPTION and INTCON registers are shown below.

Source: PIC16F688 Datasheet from Microchip

Counter Mode

Counter mode is selected by setting the TOCS bit in the OPTION register. In this mode, the Timer0 module counts the external clock pulses applied to its RA2/T0CKI pin. The counter will increment either on rising or falling edge of the clock pulses, which is software selectable by the T0SE (Timer0 Source Edge) bit of the OPTION register. If you set the T0SE bit, the timer will increment on the falling edge of every clock pulse arriving at the RA2/T0CKI pin. Again, the range of the counter can be extended by the use of the prescaler.

The maximum clock frequency at the T0CKI input is limited by the synchronization requirement with the internal clock. Each machine cycle (or instruction cycle) for a PIC microcontroller consists of four clock cycles, which are named as Q1, Q2, Q3, and Q4. The synchronization of T0CKI with the internal clock is accomplished by sampling the prescaler output on the Q2 and Q4 cycles of each machine cycle. Therefore, the external clock signal at T0CKI should remain high or low for at least half of the duration of the machine cycle (which is 2Tosc, Tosc is the period for the main oscillator), plus an additional resistor-capacitor delay of 20 ns. This determines the minimum value of the pulse width that enters through the T0CKI pin. The minimum time period of the input clock pulse is, therefore, 4Tosc + 40 ns, and the maximum frequency will be the reciprocal of this.

For example, if the main oscillator frequency is 4 MHz (Tosc 0.25 μs), the machine cycle will be 4 x Tosc = 1 μs long. An external clock signal going directly into the counter (without the prescaler) should be high for at least 2Tosc+20 ns = 520 ns and low for at least the same time, giving the total time period of 520 x 2 = 1040 ns. Therefore, the limit for maximum input frequeny would be 1/1040 ns = 961.5 KHz. If the prescaler is used, the electrical specification of PIC16F688 says that the external clock input must be high and low for at least 10 ns, which gives the maximum countable frequency through T0CKI pin equal to 50 MHz. Read Microchip's tutorials on Timers: Part 1 and Part 2 for further details.

Experimental Setup and Software

After reviewing the theory, lets think about doing some experiments with the Timer0 module. First, we will create an approximate 1 sec delay using the Timer0 module as a timer. The PIC16F688 runs at 4 MHz clock frequency, so the duration of a machine cycle is 1 μs. To generate 1 sec delay interval, the timer should count 1000000 machine cycles. If we use the prescaler value of 256, the required count will be reduced to 3906. Now, if we preload the TMR0 with 39, it will overflow after 256-39 = 217 counts. This gives the required number of overflows to make 3906 counts = 3906/217 = 18. With this setting, after every 18 overflows of TMR0 register (preloaded with 39), an approximate 1 sec interval is elapsed. The software below implements this to flash an LED with an approximate 1 sec interval.

/*

Lab 7: 1 sec timer using TIMER0
Internal Oscillator @ 4MHz, MCLR Enabled, PWRT Enabled, WDT OFF
Copyright @ Rajendra Bhatt
Nov 18, 2010
*/
// Define LED connection
sbit LED at RC0_bit;
unsigned short Num;
// Interrupt service routine
void interrupt() {
  Num ++;           // Interrupt causes Num to be incremented by 1
  if(Num == 18) {
   LED = ~LED;       // Toggle LED every sec
   Num = 0;
  }
  TMR0 = 39;        // TMR0 returns to its initial value
  INTCON.T0IF = 0;  // Bit T0IF is cleared so that the interrupt could reoccur
}
void main() {
 CMCON0 = 0x07;    // Disable Comparators
 ANSEL = 0x00;     // Disable analog channels
 TRISC = 0x00;     // PORTC O/P
 LED = 0;
 Num = 0;
 OPTION_REG = 0x07; // Prescaler (1:256) is assigned to the timer TMR0
 TMR0 = 39;          // Timer T0 counts from 39 to 255
 INTCON = 0xA0;     // Enable interrupt TMR0 and Global Interrupts
 do {
 // You main programs goes here
 } while(1);  // infinite loop
}

Download HEX file

The circuit setup is the same as Lab 1: Flashing an LED. The LED is driven through RC0 pin.

Circuit setup for flashing LED using Timer0 module

Note: The 1 sec delay that we just created is not very accurate because of the following reasons:

  • In this example, the PIC16F688 microcontroller was operated with the 4 MHz internal RC oscillator, which is not highly accurate and stable. For better accuracy, an external crystal oscillator must be used.
  • The timer program was written in a high-level language, so we don't know exactly how the program looked like after being compiled. For an accurate hardware timer, the programming must be done with assembly language, and any instruction that can affect the TMR0 read/write operation, should be accounted as it may introduce additional delay.

Next, the Timer0 module will be used as a counter to count the external clock pulses through RA2/T0CKI pin. The external clock source will be derived from the mains AC supply. The mains AC is 120V, 60 Hz sine wave signal. It will be first stepped down to 9 V, 60 Hz signal using an AC wall adapter. Before applying it to the T0CKI pin, it must be rectified and the peak voltage should be chopped down to +5V. The following circuit will convert the 9 V, 60 Hz AC voltage to an approximate +5 V square wave suitable for the T0CKI input.

The output square wave will be connected to the RA2/T0CKI pin of the PIC16F688 microcontroller. The TMR0 will start from 0 and count the incoming pulses for 1 sec. The result will be displayed on the LCD screen. The number of pulses per second is the frequency of the incoming signal, which is 60 Hz. The circuit diagram for the microcontroller and LCD part is shown below.

Counter circuit setup on the breadboard

Programming sequence involves initialization of ANSEL, CMCON0, and OPTION registers. The T0CS bit in the OPTION register must be set to operate the timer module as a counter.

/*
Lab 7: Timer0 as a counter

Internal Oscillator @ 4MHz, MCLR Enabled, PWRT Enabled, WDT OFF
Copyright @ Rajendra Bhatt
November 18, 2010
*/
// LCD module connections

sbit LCD_RS at RC4_bit;
sbit LCD_EN at RC5_bit;
sbit LCD_D4 at RC0_bit;
sbit LCD_D5 at RC1_bit;
sbit LCD_D6 at RC2_bit;
sbit LCD_D7 at RC3_bit;
sbit LCD_RS_Direction at TRISC4_bit;
sbit LCD_EN_Direction at TRISC5_bit;
sbit LCD_D4_Direction at TRISC0_bit;
sbit LCD_D5_Direction at TRISC1_bit;
sbit LCD_D6_Direction at TRISC2_bit;
sbit LCD_D7_Direction at TRISC3_bit;
// End LCD module connections
// Define Messages

char message1[] = "Frequency=   Hz";
char *freq = "00";
void Display_Freq(unsigned int freq2write) {

 freq[0] = (freq2write/10)%10 + 48;    // Extract tens digit
 freq[1] =  freq2write%10     + 48;    // Extract ones digit
 // Display Frequency on LCD
 Lcd_Out(1, 11, freq);
}
void main() {

 CMCON0 = 0x07;    // Disable Comparators
 ANSEL = 0x00;     // Disable analog channels
 TRISC = 0x00;     // PORTC O/P
 TRISA = 0b00001100; // RA2/T0CKI input, RA3 is I/P only
 OPTION_REG = 0b00101000; // Prescaler (1:1), TOCS =1 for counter mode
 Lcd_Init();                 // Initialize LCD
 Lcd_Cmd(_LCD_CLEAR);        // CLEAR display
 Lcd_Cmd(_LCD_CURSOR_OFF);   // Cursor off
 Lcd_Out(1,1,message1);      // Write message1 in 1st row
 do {

  TMR0=0;
  Delay_ms(1000);  // Delay 1 Sec
  Display_Freq(TMR0);
 } while(1);  // Infinite loop
}

Download HEX File

References:

1. Timer0 Tutorials from Microchip
2. PIC Microcontrollers (second edition) by Martin Bates
 4 50share13
 

--
With Regards,

s.m.sethupathy,
sms communication,
Tanjore -1.

mobile :9944 186 173           
      www.questionpaperlink.co.cc
      www.sethu-panguvarthagam.blogspot.com





Currently have 0 comments: