Design of LCD1602 electronic clock based on single chip microcomputer

Learning tasks:

(1) Basic understanding of LCD1602
(2) Using LCD1602 to realize minute and second timing based on 51 single chip microcomputer;
(3) Using buttons to control the adjustment of minutes and seconds (two buttons control the increase of minutes and seconds respectively);
(4) Able to realize the function of hourly timing (buzzer sounds);
(5) Understand the download module and download principle;
(6) Basically understand and use DXP to draw PCB board;

Summary of knowledge points:

1. LCD1602:

The character type liquid crystal display module is a dot matrix LCD specially used to display letters, numbers, symbols, etc. The LCD1602 used this time is 16*2 type.

1. Basic operation sequence

1.1 Read status: Input: RS=L, Rw=H, E=H Output: D0~D7=status word;
1.2 Write instruction: Input: RS=L, Rw=L, D0~D7=instruction code, E=high pulse, Output: None;
1.3 Read data: Input: RS=H, Rw=H, E=H Output: D0~D7=data;
1.4 Write data: Input: RS=L, Rw=H, D0~D7=data, E=high pulse, Output: None;

2. Status word description

STA7...STA0
D7...D0
STA0~6 are the values ​​of the current data address pointer; STA7 is the read and write operation enable, 1 is disabled, 0 is enabled;
the first line takes the address 80, the second line is 80+40;

3. Initialization settings

Display mode setting
00111000 (0x38)
Display switch and cursor setting
instruction code
00001DCB D=1 display on, D=0 off
C=1 display cursor, C=0 off
B=1 cursor flashing, B=0 off
000001NS N=1 When reading or writing an address, the character pointer increases by one, and the cursor increases by one
N=0 minus minus
S=1 write a character, the entire screen display moves left (N=1) or right (N=0) to get the cursor does not move but the screen moves
S=0 does not move

4. Indicator code

80H+address code (0-27H 40-67H) (only display the first 16 digits of each line)
01H Display clear screen: 1. Data pointer cleared 2. All displays cleared
02H Display enter: Data pointer cleared

5. Initialization process (reset process)

1. Delay 15ms
2. Write command 38H (do not detect busy signal)
3. Delay 5ms
4. Write command 38H (do not detect busy signal)
5. Delay 5ms
6. Write command 38H (do not detect busy signal)
7. Write command 38H: Display mode setting
8. Write command 08H: Display off
9. Write command 01H: Display clear
10. Write command 06H: Display cursor movement setting
11. Write command 0cH: Display on and cursor setting

2. Timer

1、TMOD

Used to set the working mode of the timer and counter. The lower four bits are used for T0 and the upper four bits are used for T1.
7 6 5 4 3 2 1 0
Byte address GATE C/T M1 M0 GATE C/T M1 M0 TMOD

GATE is the gate bit, which is used to control whether the start of the timer is affected by the external interrupt source signal. When TR0 or TR1 in TCON is set to 1 by software, the timer/counter can be started; when GATE=1, TR0 or TR1 must be set to 1 by software, and the external interrupt pin INT0/1 must also be high level to enable the timer/counter to work. That is, the start condition of the timer at this time adds the condition that the INT0/1 pin is high level;
C/T: Timing/Counting Mode Selection Bit C/T=0 is timing mode; C/T=1 is counting mode;
M1M0: Working Mode Setting Bit

There are four working modes for timer/counter:
M1M0 Working mode Description
00 1 13-bit timer/counter
01 2 16-bit timer/counter
10 3 8-bit auto-reload timer/counter
11 4 T0 is divided into two independent 8-bit timer/counters; T1 stops counting in this mode

Mode 3: Only applicable to timer/counter T0. When timer T1 is in mode 3, it is equivalent to TR1=0 and stops counting.
Mode 3 divides T0 into two independent 8-bit counters TL0 and TH0.

2. Initialization program

Assign a value to TMOD, determine the working mode of T0 and T1, calculate the initial value, and write it into the interrupt mode of
TH0, TL0 or TH1, TL1 , then assign a value to EA, open the timer interrupt to set TR0 or TR1, start the timing, counter timing or counting

learning process:

Get a basic understanding of LCD1602 and TMOD timer through videos or online materials and perform initialization operations;

analyse problem:

First, make LCD1602 able to basically display the position of minutes and seconds;
secondly, make the timer increase every second, that is, set the timer to change every second. Because the timer is 2^16us, in order to accurately adjust one position in 1s, 50ms is realized when the timer is run once, and then the seconds are increased when the timer is repeated 20 times;
when realizing the increase of minutes and seconds, it is best to stop the timer at the same time when pressing the key, that is, TR0=0, and then display the cursor and the cursor flashing, that is, 0x0f, and then increase the seconds each time you press it. The principle of adjusting the time division is the same as above. When the adjustment is completed, the cursor disappears and stops flashing (0x0c), and the timing continues to start (TR0=1).
At the same time, before the main program runs, it is best to debounce the key scan, and the minute and second program is placed before the main program;

DXP drawing PCB board

First create a project, then create a schematic diagram and PCB. Drag these two into the project and save them. Then start looking for components in the library and connect them. When connecting, make sure the pins are connected well, otherwise there will be errors when importing the PCB board. Pay attention to the packaging of components. Components without packaging will not be imported into the PCB.
After the schematic diagram is drawn, import the PCB and there are no errors. Start setting the size of the PCB board and the position and connection of the components. At the same time, the connection should not be too thin, and try to connect the wires appropriately.

Problems in the learning process

When you are stuck and have no idea in the process of writing code, you can choose to ask seniors or find experts on the Internet, and modify your own code by understanding their ideas of writing code. At the same time, the most important thing is to be careful when writing code. If the main function is wrong, the code will run and the detection will show a warning instead of an error, which will make you make a wrong judgment.
In the process of soldering the board, pay attention to the direction of the components before printing the drawings, otherwise the components will be opposite to the facts, resulting in re-soldering and waste of equipment.

Regarding the mirror image problem of PCB board:
When there are patches on PCB, the mirror image problem should be considered, because on the PCB board, the traces and packages we see are all plug-in and can be placed directly. There are two mirror images from PCB to finished product that have offset each other (one is thermally transferred to the board, and the other is the plug-in device from the reverse side of the wiring), but the patch package is placed directly from the wiring side, so the mirror image problem needs to be considered.
Single-layer board: the reverse side of the plug-in device, and the plug-in device is generally on the top of the circuit board, so the patch is on the ground of the circuit board. In this way, you only need to mirror the patch device before wiring, and the method is to make the patch symmetrical on the X axis.

code show as below:

void key_scan()

{

    if(key1==0)

    delay_50us(100);

    if(key1==0)

    {

        TR0=0;

        AN++;

        while(!key1);

    }

        if(AN==1)

        {

            write_com(0x80+0x40+8);

            write_com(0x0f);

        if(key2==0)

        delay_50us(100);

        if(key2==0)

        {

           while(!key2);

            miao++;

            if(miao==60)

            {

               beef=~beef;

                    delay_50us(10);

             miao=0;

             fen++;

                    if(fen==60)

                        fen=0;

               write_shu(4,fen);

            }

            write_shu(7,miao);

        }

        }

        if(AN==2)

        {

            write_com(0x80+0x40+5);

            write_com(0x0f);

        if(key2==0)

        delay_50us(100);

        if(key2==0)

        {

           while(!key2);

               fen++;

                if(fen==60)

             fen=0;

            write_shu(4,fen);

        }

        }

         if(AN==3)

         {

             TR0=1;

             AN=0;

             write_com(0x0c);

         }

}

void int0 () interrupt 1

{

    TH0=(65536-50000)/256;

    TL0=(65536-50000)%256;

    num++;

    if(num==20)

        {

            num=0;

            miao++;

            if(miao==60)

            {

                miao=0;

                beef=~beef;

                delay_50us(10);

                beef=~beef;

                delay_50us(10);

                beef=~beef;

                delay_50us(10);

                beef=~beef;

                delay_50us(10);

                beef=~beef;

                delay_50us(10);

                beef=~beef;

                delay_50us(10);

                fen++;

                if(fen==60)

                {

                    fen=0;

                }

            }

          write_shu(4,fen);

            write_shu(7,miao);

        }

}

void main()

{

    heat();

    while(1)

    {

        key_scan();

    }

}