MCU Experiment--Traffic Light

1. Become more familiar with the HNIST-2 single-chip microcomputer system

Related hardware circuits;

2. Master the application of microcontroller interrupts and the writing method of interrupt handling programs;

3. Master the use and programming methods of the internal timer/counter of the microcontroller

。

2. Preparation before the experiment

1. Complete homework 4

2. Write relevant programs according to the experimental content and perform Proteus simulation.

3. Experimental Content

There are three experimental items, of which the first and second items are required.

1. Basic traffic lights.

According to the circuit in Figure 3.2, the IO port of the microcontroller controls 4 groups of red, green and yellow light-emitting diodes, totaling 12, so that the light-emitting diodes emit and flash according to certain rules and orders to realize the function of simulating traffic lights. Assume that the initial state is: (north-south traffic state) north-south green light, east-west red light (25s); then turn to the transition state: north-south yellow light, east-west red light (5s); then turn to the east-west traffic state: east-west green light, north-south red light 25 (s). Then turn to the transition state: east-west yellow light, north-south red light (5s), and then cycle back and forth.

It is required to use a timer to achieve the required timing.

2. Key-controlled traffic lights.

Press the K1 key

, keep the north-south traffic status; press the K2 key

, keep the east-west traffic status; press the K3 key

, maintain normal traffic lights.

Requires keystroke processing to be performed in an interrupt.

3. With flashing traffic lights.

Increase on the basis of 2, the green light flashes for the last 5 seconds, that is, on for 0.5 seconds and off for 0.5 seconds.

4. Experimental Schematic Diagram

Figure 3.2 Traffic light experimental circuit schematic

Figure 3.2 shows a total of four buttons K1, K2, K3, and K4, which are connected to the microcontroller P2.0, P2.1, P2.2, and P2.3 pins respectively. After the button is pressed, the corresponding pin is at a low level, and is connected to P3.2 (external interrupt 0) through four diodes D17, D18, D19, and D20. This is an AND circuit composed of diodes, that is, pressing any key can generate a low level or drop on P3.2, which serves as an interrupt trigger signal.

5. Software Design Concept

1. Regular thinking.

Use timer T0 or T1 to set the timing to 500ms, interrupt and count every 500ms, count 10 times for 0.5s, count 20 times for 1s, and achieve the required timing time for the second counting.

2. Turn on the light to control your thoughts.

The microcontroller controls the lamp pins and the lamp corresponds as follows, 0 lights up.

There are four states: S0, S1, S2, and S3.

a. North-south traffic S0 state:

Green light for north-south direction, red light for east-west direction, P0= 11110111=0xf7, P1=10011110=0x9e;

Transition state S1

c. East-West Traffic Status S2:

East-west green light, north-south red light, P0=11111100=0xfc, P1=11110011=0xf3;​

 Transition state S3

Set a second counting unit SEC to +1 per second, and set two control value variables a and b.

First, set SEC=0, a=0xfd, b=0x75, in S0 state;

SEC==25, a=0xfc, b=0xf3, in S1 state;

SEC==30, a=0xfb, b=0xae, in S2 state;

SEC==55, a=0xf7, b=0x9e, in S3 state;

SEC==60, SEC=0, a=0xfd, b=0x75, in S0 state;

P0=a，P1=b。

3. Traffic light keying

After pressing the button, external interrupt 0 is entered, and the external interrupt 0 interrupt program is judged: if the K1 key is pressed, the north-south traffic state is controlled, and the timer T0 is turned off to maintain the north-south traffic state; if the K2 key is pressed, the east-west traffic state is controlled, and the timer T0 interrupt is turned off to maintain the east-west traffic state; if the K3 key is pressed, the timer T0 interrupt is turned on to restore the normal traffic light.

4. Flicker control

When flashing is required, 0.5s is displayed normally, and 0.5s is completely off, which is the flashing effect. The implementation method is: when = 0.5s, and in the last 5s (19) of north-south traffic or the last 5s (49) of east-west traffic, turn off the green light: P0 = 0xf9, P1 == 0x24, when = 1s, display normally.

6. Experimental source code

#include //Basic traffic light program

#define uint unsigned int 

uint flag = 20; // define the timer flag

uint second=0; //define the second sign 

void main()

{

TMOD=0x01; //Select T0 timer working mode 1

TH0=(65536-50000)/256; //Initial value of TH0 is 50000us

TL0=(65536-50000)%6; //Install the initial value for TH1

TR0=1; //T0 timer in SCON is turned on

ET0=1; //Open the timer counter T0 interrupt

EA=1; //Open the general interrupt

P2=0xf7; // Initialize the traffic light

P3=0x9e;

while(1) //Wait for time and react

{

if(second==25)

{ P2=0xf7;P3=0x9e; }

if(second==30)

{ P2=0xfb;P3=0xae; }

if(second==55)

{ P2=0xfc;  P3=0xf3; }

if(second==60)

{ P2=0xfd; P3=0x75; }

if(second>60) second=second`;

 }

}

void T0_int(void) interrupt 1

{

TH0=(65536-50000)/256;

TL0=(65536-50000)%6;

flag--;

if(flag==0)

{

second++; //second mark plus 1

flag=20; //Reset timer flag

}

}

#include //Basic traffic light program

#define uint unsigned int

sbit k1=P2^0;

sbit k2=P2^1;

sbit k3=P2^2;

uint flag = 5; // define the timer flag

uint second=0; //define the second sign

uint key; //A flag to determine whether a key is pressed

void main()

{

TMOD=0x01; //Select T0 timer working mode 1

TH0=(65536-5000)/256; //Install the initial value of TH0 to 50000us

TL0=(65536-5000)%6; //Install the initial value for TH1

TR0=1; //T0 timer in SCON is turned on

ET0=1; //Open the timer counter T0 interrupt

EX0=1; //Open external interrupt 0

IT0=1; //External interrupt 0 trigger mode is edge trigger

PX0=1; //Set external interrupt 0 priority to 1

EA=1; //Open the general interrupt

P1=0xf7; // Initialize the traffic light

P3=0x9e;

while(1) //Wait for time and react

{

if(second==10)

{ P1=0xf7;P3=0x9e; }

if(second==20)

{ P1=0xfb;P3=0xae; }

if(second==30)

{ P1=0xfc;  P3=0xf3; }

if(second==40)

{ P1=0xfd;  P3=0x75; }

if(second>40) second=second`;

if(key==1) { TR0=0; P1=0xf7;P3=0x9e; } //If k1 is pressed, north-south traffic

if(key==2) { TR0=0; P1=0xfc; P3=0xf3; } //If k2 is pressed, east and west pass

if(key==3) //If k3 is pressed, normal traffic light

{  

TR0=1;

TH0=(65536-5000)/256;

TL0=(65536-5000)%6;

}

 }

}

void T0_int(void) interrupt 1 //Interrupt subroutine of timer counter

{

TH0=(65536-5000)/256;

TL0=(65536-5000)%6;

flag--;

if(flag==0)

{

second++; //second mark plus 1

flag=5; //Reset timer flag

}

}

void X0_int(void) interrupt 0 //interrupt subroutine for external interrupt 0

{

if(k1==0) key=1; //Set key flags according to each key situation

if(k2==0) key=2;

if(k3==0) key=3;

}