The 8051 can be set up so that an interrupt occurs whenever tf1 or tf0 is set. Recall 8051 timer counter can count up to 65535 and 16 bits cover 65535 in binary. This document is, essentially, a compilation of all the tutorial information found on. This timer registers can count values from 0000h to ffffh which is a total of 65536 counts. The format of tmod register is, the lower four bits of tmod register is used to control timer 0 and the upper four bits are used to control timer1. There are 21 unique locations for these 21 special function registers and each of these register is of 1 byte size. How to use timer interrupt in 8051 microcontroller the. The above circuit diagram was designed in a simple way to illustrate the generation of time delay using timers in 8051 microcontroller. This is an 8bit register which is used by both timers 0 and 1 to set. This is quite similar to the rst interrupt vectors in the case of 8085. Tmod timer mode register and tcon timer control register, which are used for activating and configuring timers and counters. There are two 16bit timers and counters in 8051 microcontroller. Tmod and tcon registers are used for setting and using these timerscounters. The tcon register consists of timer overflow flags, timer run control bits, external interrupt flags and external interrupt type control bits.
In fact, by manipulating the 8051 microcontroller special function registers sfrs, you can assess or change the operating mode of the 8051 microcontroller. Generation of time delay is most important concept in embedded systems. Creating time delay using timers in 8051 microcontroller. Most of the times, we need to generate precise time delay be. This special function register psw is also bit addressable and 8 bit wide means each bit can be set or reset independently. Both the timers consist of a 16bit register in which the lower byte is stored in the tl and the higher byte is stored in the th. The code itself compiles just fine, but when i go to send the code to the 8051, nothing happens. What is the difference between timer and counter in the.
To select the operating mode and the timercounter operation of the timers we use tmod register. The tmod register is used to select the operating mode and the timercounter operation of the timers. Here port 2 was toggled from high to low and from low to high for every five seconds delay. Before learning about 8051 timer programming, you should know how to use keil for 8051 programming and how to use input put ports of 8051 microcontroller. Its lower 4 bits are used for timer0 and upper 4 bits are used for timer1.
To select the operating mode and the timer counter operation of the timers we use tmod register. In this mode, the timer register is configured as a bit register. Know about types of registers in 8051 microcontroller. Timer mode control register tmod of 8051 8031 microcontroller the tmod register is used to select the operating mode and the timer counter operation of the timers. Timers count from 0 to 255 in 8 bit mode as in 8 bit 255 is the maximum value and when timer hits the 255 number then we say that our timer is overflowed. Since the 8051 follows an 8bit architecture, each 16 bit is accessed as two separate registers of lowbyte and highbyte.
Feb 05, 20 counters and timers tuesday, february 05, 20 8051 architecture 4 comments many microcontroller applications require the counting of external events, such as the frequency of a pulse train, or the generation of precise internal time delays between computer actions. Apr 05, 2018 in this project, i will discuss a little bit about timers in 8051 microcontroller and also how to generate a delay using 8051 timers. Flag register in 8051 is called as program status word psw. When used as counters, the microcontroller counts the external clock pulses provided on pin 3. It is used by the 8051 to access external memory using the address indicated by dptr. Since 8051 has 8bit architecture, each of these is accessed by two separate 8bit registers as shown in the figure below. Tmod is an 8bit register used for selecting timer or counter and mode of timers. A timer module for an 8051 microcontroller is designed from the ground up. I said 8051 is a 8bit controller and both timers are 16bit timer. The data pointer dptr is the 8051s only useraccessible 16bit 2byte register. This application note provides a programming example of how to use the standard 8051 timer 0 in an interrupt to generate a timertick. Since 8051 89c51,89 c52 is an 8bit microcontroller, so to load 65535 we need two registers one representing the high byte and other the low byte. In the case of timers, register is incremented once every machine cycle. Since we can use them as counters so we can easily generate timedelays and baud rate for serial uart communication.
Jan 26, 2016 as i explained earlier, we are gonna use timer interrupt in 8051 microcontroller. Counters and timers in 8051 microcontroller contain two special function registers. Timers can be based on internal clock osc6 or from external source counter mode. Jan 22, 2014 so to do this 8051 has packed with timers which is capable of generating required time delay and can serve as a counter. What is difference between timer and counter in 8051. Timer 0 and timer 1 are two timer registers in 8051. If the program size is more than 4 k bytes 8051 will fetch the code automatically from external memory. Aug 08, 2019 805189c51,89c52 series microcontrollers have two build in timers, timer0 and timer1. The 80518052 microcontroller architecture, assembly language, and hardware interfacing craig steiner universal publishers boca raton, florida. The 8051 has two counters timers which can be used either as timer to generate a time delay or as counter to count events happening outside the microcontroller. Both of these registers use the same register called tmod to set various timer operation modes. It is used to count the events happening outside the microcontroller.
Whenever its input pulses, the 8051 decrements the counter value. Jun 26, 2018 8051 has two 16bit timers, which can also be used as counters by setting the appropriate bits in the tmod registers. How to use internal timer registers of 805189c51,89c52. Timer mode control register tmod of 80518031 microcontroller the tmod register is used to select the operating mode and the timercounter operation of the timers. Aug 18, 2018 both timers and counters in 8051 microcontroller in mode 0 is an 8bit counter with a divideby32 prescaler. As the name says, timers are used for time and counting. Each one of these is assigned an interrupt vector address. Since the 8051 has an 8bit architecture, each 16bit is accessed as two separate registers of low byte and high byte. Accumulator is an 8 bit register widely used for all arithmetic and logical operations. Microcontrollers notes for iv sem ecetce students saneesh. Cpu registers provide explanations to the following register types. Timers and counters are so integral that you will see numerous examples involving them throughout this series.
Tmod is an 8bit register used to set timer mode of timer0 and timer1. Timercounter mode control tmod register, bits 2 and 6 respectively. Nov 17, 2017 8051 timer section bharat acharya education bharat acharya education. And the code doesnt do much right now, its suppose to just play one note over and over again forever, but nothing happens. Apr 20, 2019 these two registers th and tl are timer high byte and timer low byte, 0 and 1 are the timers numbers. The 8051 microcontroller consists of two 16bit timers and counters such as timer 0 and timer 1. Both timers consist of 16bit register in which the lower byte is stored in tl and the higher byte is stored in th. The 8051 architecture can handle interrupts from 5 sources. What is the counting rate of a machine cycle in correlation to the oscillator frequency for timers. When their count rolls over from the maximum count to 0000, they set the corresponding timer. Counting and timing allows you to do some very neat things such as controlling. Timers and counters in 8051 microcontroller baud rate.48 980 1274 960 1328 1087 1090 495 413 1059 1425 920 64 877 1280 942 1269 579 503 939 1043 1513 1513 1182 717 561 1391 561 919 1387 1239 821 426 1252 1191