Using the 51 series single chip microcomputer timer function to measure pulse width

The STC12C series enhanced MCU expands the functions of the basic 51 MCU on-chip, such as providing a PCA/PWM interface, and the timer can work in 1T mode (the clock of the basic 51 MCU is 12-divided by Fosc, and 1-divided in 1T mode).

PCA can be used to measure pulse width. However, protues does not currently support the simulation function of this series of microcontrollers, and repeated burning is also very troublesome, so it is better to use the basic 51 microcontroller to implement this function first, and then implement PCA to measure pulse width in the following blog post.

The implementation ideas are as follows:

After the highest bit GATEn of TMOD is set, Tn starts counting and is affected by INTn (Pin3.3) and TRn: TRn is 1, and Tn is allowed to count only when the INTn pin input is high. This function can be used to measure the width of the positive pulse on INTn.

First, here's the picture (forgive my drawing skills):

1):1 before the rising edge, initialize TMOD, TRn=1;

2): INTn pin at 2 is at high level, and starts counting and measuring pulse width;

3): INTn pin at 3 is at low level, measurement ends and counting stops TRn=0

 

Here is the simulation picture:

1). Select 5v square wave as the signal generator level. Note that the inverting end of the signal generator is grounded, otherwise the positive end will only output a 2.5v square wave (the remaining 2.5v outputs an inverted square wave, which can be connected to an oscilloscope for a try), and INTn will never receive a high level, and the expected effect will not be achieved.

2). The T0 timer is used as a counter, and an overflow occurs when a negative pulse is received, which starts T1;

3). T0 and T1 all work in mode 2 automatic loading count value mode.

Then, the code:

Working frequency 12Mhz

 

#include 
#include 

sbit P1_0 = P3^3;

#define MakeByte(target, Hi,Lo) \
do{ \
	target |= (((Hi)<<4)|(Lo)); \	
}while(0); \

#define SetTH(n,val) \
do{ \
	TH##n = val; \
}while(0); \

#define SetTL(n,val) \
do{ \
	TL##n = val; \
}while(0); \

#define EnableET(n) \
do{ \
	ET##n = 0x01; \
	IE |= 0x80; \
}while(0); \

unsigned int click;  
unsigned int oneMs;
unsigned char getPlusWidth;
int main()
{
	unsigned int totalus=0,maxPlusWidth=0;
	P3 = 0xFF;

	getPlusWidth = 0;
	MakeByte(TMOD,0x0A,0x06);
	SetTH(0,0xff);
	SetTL(0,0xff);
	SetTH(1,0x38);
	SetTL(1,0x38);
	EnableET(0);
	EnableET(1);
	TR0 = 0x01;
	while(1)
	{
		while(!getPlusWidth);
		//Wait for INT1 to go low
		while(INT1==0x01);
		//Wait for INT1 to reach high level
		while(INT1==0x00);
		//Wait for INT1 to be low level, pulse width ends
		while(INT1==0x01);
		TR1 = 0x00;

		totalus = 1000*(oneMs+(click*0.2))+(TL1-TH1);	
		oneMs = 0;
	}
	return 0;
}

//T0 pin receives negative transition
void IsrT0() interrupt 1
{
	TR1 = 0x00;
	getPlusWidth = 1;		
	TR1 = 0x01;
}

void IsrT1() interrupt 3
{
	//Each interruption is 0.2ms
	click++;
	if(click == 5)
	{
		oneMs++;
		click=0;
	}
}

Finally, the simulation results are:

 

500Hz square wave, pulse width 981us

1kHz square wave, pulse width 587us

2kHz square wave, pulse width 234us