When the counter is running on an external clock source (may be a periodic or aperiodic external signal) it is called a “Counter” itself and it can be used for counting external events. When the counter is running on the processor’s clock, it is called a “Timer”, which counts a predefined number of processor clock pulses and generates a programmable delay. Delay using timer is the most accurate and surely the best method.Ī timer can be generalized as a multi-bit counter which increments/decrements itself on receiving a clock signal and produces an interrupt signal up on roll over. Generating delay using pure software loops have been already discussed here but such delays are poor in accuracy and cannot be used in sensitive applications. Actually i calculated the delay values for 2 ms and loaded the calculated values for TH and TL registers in them.The 8051 microcontroller has two independent 16 bit up counting timers named Timer 0 and Timer 1 and this article is about generating time delays using the 8051 timers. Now if you took the tutorial you are thinking what’s going on in delay() function. How to use internal timers of 8051 microcontroller for generating fixed delays.Also you will be able to know about the TMOD(Timer Mode) register bits. If you don’t go through the lesson then hurry up and take it

You can calculate the values for TH and TL registers by using the formula given in the tutorial. The main thing in the code is delay() function & how is it working? To understand it you should know about the internal timer registers and i hope you take the tutorial mentioned above.

Whole of this part is placed in while(1) loop making the Statements to execute for ever. This means led will glow for 1 second and then turn off for 1 second. led=0 is switching off our led after 1 second. delay() function is something that is the topic of this tutorial. Statement P1=0x00 is initializing Port-1 as Output. Then the statement sbit led=P1^0 is assigning Port-1 bit#0 a variable led.Ĭoming to main function.

reg51.h is the header file necessary to be included in every project which is using keil(software) for writing and compiling code. First in code i included the header file.

8051 timer calculation