51 timer initial value calculation

#define FOSC 11059200L

#define T1MS (65536-FOSC/12/1000)   //1ms timer calculation method in 12T mode

 

stay 51 See such a code in the technical manual of single chip microcomputer ,

It means , Timer implementation 1 Millisecond timing , Find the initial value of the timer .

Because the timer counts 65536 after , It will be cleared , Want to achieve specific timing , You have to calculate the starting point by yourself , Also called initial value

because 1 One machine cycle is equal to 12 Clock cycles , therefore FOSC/12, What you get is the frequency of a machine cycle , It's also 1 The number of seconds counted by the timer , Divided by 1000, Namely 1 The number of timers counted in milliseconds .

Want the timer to clear after these numbers , Set the starting point as 65536- The number .

 

So you get 65536-FOSC/12/1000

 

Empathy , Want to set 5 Millisecond timer ,65536-5*FOSC/12/1000

 

In this way, I get , Want to set t Millisecond timer ,65536-t*FOSC/12/1000

Be careful , The timer has an upper limit , The maximum is 65536*FOSC/12 millisecond , Because a machine cycle is FOSC/12 millisecond , The timer counts at most 65536 Time , Will overflow , from 0 Start counting .