Micro controller timer functioning ?

[agnivesh]

considering each machine cycle of 8051 consisting of 12 external oscillator pulses and, let's say external oscillator frequency is 'f', then each machine cycle will take 12/f seconds to complete (am i right ?). timers and counters use this machine cycle to increment the registor bits.

how timers use this info to calculate 1 sec time interval ?
how timers adapt to calculate 1 sec time interval again if we change the external oscillator frequency ?

when we write code, we say wait for 'n' seconds and then raise 'x' pin state to logic 1, how microcontroller calculates those 'n' seconds interval ? how it will calculate the same n second interval if we change the external oscilllator frequency ?

with regards
agnivesh

 

[hm_fa_da]

yes it is true , if you are using 8051 family , timer counts one up each F/12
but if you are using a compiler , when you say wait for 1s , you should say how much your osciator frequency is . then compiler calculates number that should be loaded to timer and places it in your program .

if you change oscilator frequency , for example if you enter 12MH in your compiler as oscilator frequency , and when you are using MCU , you use 24MH crystal , then 1s would be 0.5s.

regards.