Introduction to single chip microcomputer - basic control of LED indicator light

Implementation process

74HC138 decoder (38 decoder) -> 74HC02 NOR gate -> 74HC573 latch

38 decoder

Three inputs control eight mutually exclusive low-effective outputs (three P2 ports control eight Y ports, controlling Y4 to output a low level)

74HC02 NOR Gate

After Y4 outputs a low level, it passes through the NOR gate. At this time, WR is a low level (using the I/O expansion method), and Y4C inputs a high level, that is, LE is a high level (equivalent to making the latch work). Only then can the LED light up. As for the encoding form of the P0 port, I will not write it (this is very simple)

74HC573 Latch

OE: Output Enable

LE: Latch Enable

(I haven't learned these two yet, so it won't affect my study)

Come to update,

D is the input terminal and Q is the output terminal

Note that there is a horizontal bar on OE, which means that the low level is valid (that is, the circuit will work only when the level is low), so OE is connected to the GND terminal

When Y4C inputs a high level, that is, LE is a high level, the state of the Q terminal is determined by the state of the D terminal; when LE is a low level, at this time, no matter what state D is, Q maintains the previous data state.

as the picture shows:

74HC573 Latch

74HC138 decoder (38 decoder) and 74HC02 NOR gate

Different pin connections of J5, J2, and J13 jumper caps (I will update the pin connections later when I learn more)

Jumper cap connection method (connection method of this program): J5 connects to KBD terminal J13 connects to I/O port J2 connects to 2-4 1-3 terminal

code show as below:

#include

//sbit HC138_C=P2^7;

//sbit HC138_B=P2^6;

//sbit HC138_A=P2^5;

void Delay(unsigned int t){//delay function

while(t--);

    while(t--);

}

void LEDrunning() //The LED light flashes three times, then runs in the form of a running light, and repeats the above operation continuously

{

  unsigned char i;

// HC138_C=1;

  //HC138_B=0;

// HC138_A=0;

//The commented code has the same effect as the code for opening and closing registers

  P2 = (P2&0x1F|0x80); //Open register

  for(i=0;i<3;i++)

{

P0=0x00; //LED lights fully on

Delay(60000);

Delay(60000);

P0=0xff; //LED lights are all off

Delay(60000);

Delay(60000);

}

//The following two for loops form the LED light water light form

for(i=1;i<=8;i++){

P0=0xff< Delay(60000);

Delay(60000);

}

for(i=1;i<=8;i++){

P0= ~(0xff< Delay(60000);

Delay(60000);

}

P2 &= 0x1F; //Close register

}

void cls_buzz(void) //Turn off the buzzer

{

P2 = (P2&0x1F|0xA0);

P0 = 0x00;

P2 &= 0x1F;

}

void main()

{

cls_buzz();

while(1){

LEDrunning();

}

}

This is basically how you control the display of LED lights. I will update this later when I learn more.

Come to update,

Turn off peripherals

void cls_buzz(void) //Turn off the buzzer

{

P2 = (P2&0x1F|0xA0);

P0 = 0x00;

P2 &= 0x1F;

}

P2 = (P2&0x1F|0xA0);

0x1F is written as 0001 1111 in binary. The default state of P2 port is 1111 1111. P2&0x1f is to clear the upper three bits to 0, because we only need to control the three ports P7-5 in the current register. 0xA0 is 1010 0000. This code is to make Y5 low level, and make Y5C input high level through the NOR gate to control the Y5C latch (as shown in the figure)

P0 = 0x00;

ULN2003, equivalent to a NOT gate, turns off the buzzer and relay (see the buzzer and relay in this column for details)

P2 &= 0x1F;

Close, the use of this register ends

Open the register to use the LED

P2 = (P2&0x1F|0x80); //Open register

This is to open the Y4C latch

P2 &= 0x1F; //Close register

Close the Y4C latch