Timer Programming in 8051 Micro Controller with Keil

Learn More about Interrupt, timer and Serial Programming in 8051 Micro Controller : Click here

•      The 8051 has two timers/counters, they can be used either as

–     Timers to generate a time delay

–     or as Event counters to count events happening outside the microcontroller

•      Both Timer 0 and Timer 1 are 16 bits wide.

•      Since 8051 has an 8-bit architecture, each 16-bits timer is accessed as two separate registers of low byte and high byte.

–     The low byte register is called TL0/TL1 and

–     The high byte register is called TH0/TH1

The 8051 has two timers/counters, they can be used either as 

–     Timers to generate a time delay

–     or as Event counters to count events happening outside the microcontroller.

Both Timer 0 and Timer 1 are 16 bits wide.

•      Since 8051 has an 8-bit architecture, each 16-bits timer is accessed as two separate registers of low byte and high byte.

–     The low byte register is called TL0/TL1 and

–     The high byte register is called TH0/TH1

Both timers 0 and 1 use the same register, called TMOD (timer mode), to set the   various timer operation modes.

                             8051 Micro Controller Timer mode 1 programming

•      The following are the characteristics and operations of mode1:

–     It is a 16-bit timer; therefore, it allows value of 0000 to FFFFH to be loaded into the timer’s register TL and TH

–     After TH and TL are loaded with a 16-bit initial value, the timer must be started

–     This is done by setting high TR0 for timer0 and  TR1 for timer1

–     After the timer is started, it starts to count up

–     It counts up until it reaches its limit of FFFFH

–     When it rolls over from FFFFH to 0000, it sets high a flag bit called TF (timer flag).Each timer has its own timer flag: TF0 for timer 0, and TF1 for timer 1.

–     When this timer flag is raised, one option would be to stop the timer.

–     After the timer reaches its limit and rolls over, in order to repeat the process TH and TL must be reloaded with the original value, and TF must be reloaded to 0.

                             8051 Micro Controller Delay generation process

1.      Load the TMOD value register indicating which timer (timer 0 or timer 1) is to be used and which timer mode (0 or 1) is selected.

2.      Load registers TL and TH with initial count value.

3.      Start the timer.

4.      Keep monitoring the timer flag (TF). if it is raised,

5.      ƒStop the timer.

6.      Clear the TF flag for the next round

7.      Go back to Step 2 to load TH and TL again.

How to calculate values to be loaded into TH and TL 

Assume XTAL = 11.0592 MHz, we can use the following steps for finding the TH and TL registers’ values,

1.      Divide the desired time delay by 1.085 us.

2.      Calculate 65536 – n, where n is the decimal value we got in Step1.

3.      Convert the result of Step2 to hex, where yyxx is the initial hex value to be loaded into the timer’s register

4.      Set TL = xx and TH = yy.

Some Examples of 8051 Micro Controller Programming in Keil Micro Vision 4

To create a program in keil follow the following steps:

a.      Get the Keil MicroVision 4 from keil.com and install it on your computer.

b.      Click the project tab and create a new project.

c.      Select the microcontroller.

d.      Microcontroller here I will be using is AT 89C51

e.      Then Click create.

f.       From the Flash tab select Configure Flash Tools.

g.      Inside the new window, inside the Target Tab Check the Use the onchip Rom Option.

h.      Select Code Rom Size: less than 2k memory for Small programs.

i.        Give the Crystal Frequency 11.0592 mhz.

j.        Inside the Output Tab Check the Create a hex file to create a hex file.

k.      Add a C code file (.c file ) to your project by Rt Clicking the project.

/* Write a program to Toggle (on/Off) bits of Port 2(P2) continuously forever with delay. */ # include <regx51.h>  void main()  {             int i;             P2=0x00;             while(1)             {                         P2= 0x00;                         for(i=0;i<15000;i++);                         P2=0xFF;                         for(i=0;i<15000;i++);             }           }

/* Write a program to on/off leds connected in port1 using Push Switches Sw1 (used as on switch) connected to p2.0 pin  and SW2 used as off switch connected to p2.1  */  # include <regx51.h>  void main()  {             int i;             P1=0x00;             P2=0x00;             while(1)             {                         if (P2_1==1 && P2_0==0)                                     P1=0xFF;                         else                                     P1=0x00;                         for(i=0;i<10000;i++);             }  }

/* Write a program to display count 0 to 9 in 7-Segment display with the timing interval of 1 sec. Use Timer 0, 16 bit mode to generate the delay. 7 Segment display is connected to P1. */ #include <regx51.h> void delay1ms(unsigned int i) {                        int c=0;             while(c<i)             {                           TMOD=0x01;                           TH0=0xFC;                           TL0=0x66;                           TR0= 1;                           while(!TF0);                                     TR0=0;                                     TF0=0;                                      c++;             } } void main() {             P1=0x00;             while(1)             {                         P1=0xC0;                         delay1ms(1000);                         P1=0xF9;                         delay1ms(1000);                         P1=0xA4;                         delay1ms(1000);                         P1=0xB0;                         delay1ms(1000);                         P1=0x99;                         delay1ms(1000);                         P1=0x92;                         delay1ms(1000);                         P1=0x82;                         delay1ms(1000);                         P1=0xF8;                         delay1ms(1000);                         P1=0x80;                         delay1ms(1000);                         P1=0x98;                         delay1ms(1000);             } }