C51 Manual Calculation Timer Interrupt Introduction

The following is calculated by software: 12M crystal oscillator, timer mode 16 bit, 12T, 1 millisecond time

void Timer0Init(void) //1 millisecond@12.000MHz{
	AUXR &= 0x7F; //Timer clock 12T mode
	TMOD &= 0xF0; //Set timer mode
	TMOD |= 0x01; //Set timer mode
	TL0 = 0x18; //Set the initial timing value
	TH0 = 0xFC; //Set the initial timing value
	TF0 = 0; // Clear TF0 flag
	TR0 = 1; //Timer 0 starts timing}1.2.3.4.5.6.7.8.9.10.

Verify the software's results:                       

The crystal oscillator is 12M, and one oscillation takes (1/12M) seconds.

A machine cycle of a 12T microcontroller is 12 clock cycles (0.000001 seconds).

The time consumed by a 12M crystal oscillator 12T to work in one machine cycle is (1/12M)*12 seconds = 0.000001 seconds = 1 microsecond

The delay requirement is 1 millisecond, which is 1000 microseconds.

The lower 8 bits and the upper 8 bits are 16 bits in total, 65535, which can only hold 65535 microseconds of time.

THX=(65536-1000)/256=252=0xFC

TLX=(65536-1000)%256 =18=0x18

【Manual calculation】 Use 11.0592M to delay 20 milliseconds                               

20 milliseconds = 0.02 seconds

One machine cycle takes (12/(11.0592*10^6)) seconds

The cycle used for 0.02 seconds = 0.02/(12/(11.0592*10^6)) = 18432 machine cycles

11.0592M 12T 1 bit 20 milliseconds

TH0=(65536-18432)/256=0xB8

TH0=(65536-18432)%256=0x00

The software verifies my calculations:   

void Timer0Init(void) //20 milliseconds @ 11.0592MHz {
	AUXR &= 0x7F; //Timer clock 12T mode
	TMOD &= 0xF0; //Set timer mode
	TMOD |= 0x01; //Set timer mode
	TL0 = 0x00; //Set the initial timing value
	TH0 = 0xB8; //Set the initial value of timing
	TF0 = 0; // Clear TF0 flag
	TR0 = 1; //Timer 0 starts timing}1.2.3.4.5.6.7.8.9.10.

EA---Global enable bit.

EA=1, turn on the global interrupt control. Under this condition, each interrupt control bit determines whether the corresponding interrupt is turned on or off.

EA=0, turn off all interrupts.

ET2---Timer/Counter 2 interrupt enable bit.     

ET2=1, turn on T2 interrupt.              

ET2=0, turn off T2 interrupt.                  

ES---Serial port interrupt enable bit.              

ES=1, turn on serial port interrupt.           

ES=0, turn off serial port interrupt.           

ET1---Timer/Counter 1 interrupt enable bit.     

ET1=1, turn on T1 interrupt.

ET1=0, turn off T1 interrupt.

EX1---External interrupt 1 interrupt enable bit.

EX1=1, turn on external interrupt 1 interrupt.

EX1=0, turn off external interrupt 1.

ET0---Timer/Counter 0 interrupt enable bit.

ET0=1, turn on T0 interrupt.

ET0=0, turn off T0 interrupt.

EX0---External interrupt 0 interrupt enable bit.

EX0=1, turn on external interrupt 0 interrupt.

EX0=0, turn off external interrupt 0.