Blue Bridge Cup Guoxin Changtian single chip microcomputer -- led lamp module (V)

LED Etc

The whole idea
adopt 74HC138 Chip and 74HC02 Chip input high and low level , To control Y4C by 1 or 0. When Y4C by 1 when , To be approved P0 Port to control LED The light goes on and off . When Y4C by 0 when , beyond control LED The light goes on and off . Such as ： Make P27 by 1、P26 by 0、P25 by 0, The output Y4 by 0, Re pass 74HC02 chip , take Y4 by 0 Input , be Y4C Output is 1. Re pass P0 by 0xfe namely Q8-Q1, by 1111 1110, control L1 bright . Can also order P0 by 0x00 namely Q8-Q1, by 0000 0000, control L1~L8 On at the same time .

LED Control step decomposition ：
Step one ：
from CT107D Found in the schematic diagram of single chip microcomputer comprehensive training platform LED modular

According to the schematic diagram , We can know , The anode of this group of light-emitting diodes , A high level has been given , So as long as we give a low level at the cathode , You can make the diode light up .
Did you learn 51 Our friends all know , To give a low level , We just need to make IO The mouth is 0, That's all right. . namely

P0 = 0x00; // Light all LED

But what? , This board , You directly ordered P0 The mouth is 0, It cannot be lit IO Oral . stay P0 There is a chip between the port and the LED 74HC573（ Latch ）. Module detailed view Blue Bridge Cup Guoxin Changtian MCU – A detailed explanation of the schematic diagram （ Four ）
Step two ：
There is... On the board 4 slice 74HC573 chip , Enable one Y4C port （ Setting high level can control the chip ）, utilize 138 The decoder sets the high and low level of the port .

138 The function of the decoder here is to use P25,P26,P27, That is to say P2 The upper three digits of the mouth control the selected position .

Can make P27-p25 Zero clearing , Reorientation Y4C operation

P2 = P2 & 0x1F | 0x80; //P27-p25  Zero clearing , Reorientation Y4C
P2 &= 0x1F;            //P27-p25  Zero clearing 

IO Programming lights up LED The core code is as follows ：

P2 = ((P2&0x1F)|0x80);
P0 = 0x00; // Light all LED
P2 = P2 & 0x1F;

Case study ：
LED flashing

#include "reg52.h" // Definition 51 MCU special function register 

// The time delay function 
void delay(void)
{
    
    unsigned char i,j,k;
    for(i=0; i<20; i++)
    {
    
        for(j=0; j<20; j++)
        {
    
            for(k=0; k<248; k++);
        }
    }
}
// The main function 
void main(void)
{
    
    while(1)
    {
    
        P2 = ((P2&0x1f)|0x80);
        P0 = 0xff;  //LED Extinguish 
        P2 &= 0x1f;
        delay();

        P2 = ((P2&0x1f)|0x80);
        P0 = 0x00;  //LED Lighten up 
        P2 &= 0x1f;
        delay();
    }
}