51 single chip microcomputer_ External interrupt and timer / Counter interrupt

introduction

Learning SCM for some time , I don't quite understand the knowledge of interruption , I also read a lot of information on the Internet , Understand the general meaning of interrupt , For example, one of them ： You call again LOL Man-machine , Suddenly the water heater at home turned on , You must pause first LOL, Go to the water heater first , To avoid unnecessary safety accidents caused by overheating of the water heater , When you handle the water heater properly , You call again LOL, It's called ： The treatment of the water heater is interrupted . This is actually very general . Let's talk about it in detail here ： The simplest are external interrupts and timer interrupts .

External interrupt

External interrupt In fact, it belongs to key processing , The most famous external interrupts are IT0 了 , if IT0 The assignment is 0, This button is actually a low level trigger ; if IT0 The assignment is 1, This button is actually triggered by the bottom edge .（ Here is an ad ： What is the difference between low level trigger and lower edge trigger ？ Low level trigger means that the key is at low level , The code in the external interrupt function will be executed , The interrupt is always valid as long as the pin is low , Will continue to enter the interrupt , Until the level changes to high , Only by interrupting the incident can we give up ; The lower edge trigger must change from high level trigger to low level trigger , in other words , The pin remains low / High level , Nor can it be triggered more than once , Only one interrupt can be triggered . summary , Press the key once , Low level trigger mode can trigger one or more external interrupts , The lower edge trigger can trigger only one external interrupt ） This is the external interrupt .（ Here is an advertisement ： External interrupt , Generated for button events ！） So here comes the question , Button press events can be handled with external interrupts , What else can I do ？ It's simple , Directly in main In the function ：

if(key1 == 0)
		{
    
			delay10ms();
			if(key1 == 0)	// There was a button pressed 
			{
    
				 Write down that you press someone else's button key1 What are you doing 
			}
		}

---

That's all External interrupt

Next, let's talk about Timer interrupt ：

Timer interrupt

A timer is actually a countdown , And timer T0 and T1 The corresponding pins are P3.4 and P3.5.

（ Insert an advertisement ：EA Represents the main gate , Whether it's an external interrupt , Or the timer interrupt should be started , First of all EA Gate opening , The external interrupt or timer interrupt can be operated only after the switch is opened .）

A counter is actually a count down , The registers commonly used by counters are TL0,TH0,TL1,TH1. With TL0 and TH0 For example ,TL0 and TH0 All are 8 Bit register , from TL0 and TH0 Form high and low octet registers , Used to count , altogether 16 position . The scope is 0~65535, altogether 65536（2 Of 16 Power ）.

TCON register ：
Here we only talk about timing / Counter section ！
TF1 For the timer 1 Overflow position ,TR1 For the timer 1 Control bits （ On or off ）;TF0 For the timer 0 Overflow position ,TR0 For the timer 0 Control bits （ On or off ）.

IE register ：
Here we only talk about timing / Counter section ！
ET1： Timer 1 Interrupt switch
ET0： Timer 0 Interrupt switch

TMOD register ：
There are two timers , They are timers 0 And timers 1
There are two groups GATE,C/T,M1,M0;
among ,GATE Door call control position , Beginners directly make him equal to 0 that will do , And then let TR0 or TR1 be equal to 1, Corresponding timer T0 or T1 And it started .
C/T：0 Is timed ,1 For count .
final M0 and M1 I watched it together , There are four cases , Respectively 00,01,10,11 , Beginners use 01 that will do , Express 16 Bit timer / Counter , The maximum count is 2^16 = 65536
in summary ,TMOD The most commonly used is 0X01.（ namely TMOD The binary representation of the register is ：0000 0001, Just let TR0 or TR1 be equal to 1, Corresponding timer T0 or T1 And it starts , At the same time, the range is 0～65535, common 65536 Number ）

In addition, I'm adding ： How to calculate the initial value of the timer ：
65536 - 10000 = 55536 , intend Counter from 65536 Down to 55536 The time taken is 10ms.
55536 The hexadecimal of is 0xD8F0,
So set TH0 = 0XD8,TL0=0XF0,
in other words , The initial value is set to 0xD8F0, Then every 10ms Just trigger the timer once 0 or 1 interrupt

// Understand the above knowledge points , You should be able to understand the following code ！
#include<reg52.h>
sbit LED0=P1^0;
unsigned char i;
 
void main()
{
    
	TMOD=0X01;  // Set the use timer 0,16 Bit timing / Count register 
	TL0=0xD8;    // The lower octet gives the initial value 
	TH0=0XF0;    // The high octave gives the initial value 
	ET0=1;          // Turn on timer 0 interrupt 
	TR0=1;         // Run timer 0
	EA=1;          // Turn on the main interrupt switch 
	while(1);
}
 
void Delay(void) interrupt 1 using 0
{
    
	i++;
	TR0=0;           // When entering the interrupt function , off timer 
	TL0=0XD8;    // Reset the initial value 
	TH0=0XF0;
	if(i==20)        // because 10ms One trigger does not show obvious results , So let 20 The light changes only once after being triggered 
	{
    
		LED0=~LED0;
	}
	TR0=1;     // Turn the timer back on 
}

（ Finally, I'd like to add ：
timing / The working principle of the counter is to count .
When counting internal clock pulses , As timer ; When counting external pulse signal , Is the counter . Whether as a timer or a counter , It's all counters in essence .
therefore , Beginners don't have to worry about whether to use a timer or a counter , Because the two are actually the same thing , Only one is the internal clock pulse , One is an external pulse ,
therefore , Beginners use timers T0,T1 The internal pulse of is right , That is to let C/T=0 That's it ！
）