<> Difficult things can't be learned because simple knowledge isn't learned well
<> The foundation is not solid , the earth trembled and the mountains swayed
<> Key
<>1.1 Basic review
（1） Physical structure of keys
（2） There are two states of MCU pin （I/O） input 【 read 】 Or output 【 write 】
（3） Function of pull up resistor . Pull the pin up to a certain high level through the resistance , But the pull-up energy can't hold it . The pull-down force is relatively strong , The power of grounding is infinite !
（4） The meaning of keys ： A button is an input device ,CPU Connected by a key IO The level state of the pin can judge what we have done to the button , Press or pop .
（5）CPU How to detect keys ： Polling and interrupting
polled ：CPU Check to see if the key is pressed after a period of time , If the key is pressed, the key is handled , If not, check again when the next polling time is up .
Interrupted :
（6） Classification and connection of keys ：
Matrix button
Independent key
<>1.2 Independent key explanation
eg :sbit key = P0^0;
（1） Give variable key assignment , It's like asking this IO Port output , Direct use 【 read 】 The value of this variable , It's like starting from this IO Pin in .
（2） Independent buttons can press multiple buttons at the same time , The matrix button is not allowed .
（3） You can have a bit variable to control the key , It can also be controlled by port .
<>1.3 Key value detection and display
（1） What is a key value ： There are many buttons in a product , The program encodes the keys , Each key corresponds to a code value , The code value is the key value .
（2） The key detection part and the key processing part are connected by the key value .
<>1.4 shake
（1） What is jitter ： The level change of uncertainty at the moment when the key is pressed and bounced .
（2） The harm of jitter ： Judgment of interference normal level .
（3） Eliminate the scuttle ： Software and hardware chattering elimination
<>1.5 Complete key detection
<>1.5.1 A complete key event
（1） Key events are different states of the key process （ Press and pop ） Switch of
（2） A complete button state includes press event and pop-up event （ Change and switch of level ）
（3） It is generally believed that a complete key event is a real key , The program will handle the key , Therefore, the general press and lift after the button is an effective button .
<>1.5.2 Code practice
#include <reg51.h> /* connection ： P1 Port connection key key1-key8 key1:P1^0 …… key8:P1^7 P0 Port connected to independent digital tube .
function ： It is divided into two parts ： Key detection and key processing . Key detection --- Get the corresponding key value --- Do different things according to different key values . */ sbit key1 = P1^0; void
delay(unsigned char t); void display(void); void delay10ms(void); // Display of independent digital tube 0-F
unsigned char varry[16] = {0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,
0x80,0x90,0x88,0x83,0xc6,0xA1,0x86,0x8e}; unsigned char keynum = 0; void
main(void) { unsigned char flag = 0; // Flag bit , It's when it's not pressed 0, It's when you press it 1 // realization key1 Click the number plus 1
, And it's after pressing plus immediately plus 1, I can't say anything after I lift it up while(1) { if(key1 == 0) { delay10ms(); if(key1 == 0)
// There was a button pressed { if(flag == 0) { display(); flag = 1; // Key status flag position 1 } } } else
// The key is up , The button is not pressed at this time { delay10ms(); flag = 0; } delay10ms(); } } void
delay(unsigned char t) { unsigned char i,j; for(i=0;i<t;i++) for(j=0;j<t;j++);
} void display(void) { P0 = varry[keynum]; keynum += 1; if(keynum> 15) keynum =
0; } void delay10ms(void) // error 0us { unsigned char a,b,c; for(c=5;c>0;c--)
for(b=4;b>0;b--) for(a=248;a>0;a--); }
The logic of this program is this ： First of all, check that there is a button pressed —> When the flag bit is in the default state, press the key to display the content and set the flag position 1（ Place 1 After that, even when the button is pressed, the display state is still the original state , It doesn't jump continuously ）-----> Check the status of key lifting （ When it's true ）, Flag bit reset .
<>1.6 Introduction of interruption
（1） Mainline task and interrupt task
Main task ： It's busy for a long time, but it's not very urgent
Interrupt task ： Time is short and busy
（2） Interrupt mode is more suitable for handling asynchronous events than rotation mode , More efficient .
<>1.7 AT89C51 interrupt
（1） Interrupt trigger mode ： Falling edge trigger and low level trigger
（2） Practical training
<>1.8 Matrix keyboard
（1） The pins on both sides of the matrix keyboard are connected to the MCU pins , The independent button is connected to the MCU pin while grounding .
（2） Matrix keyboard Province IO mouth
（3） The matrix keyboard does not support simultaneous pressing
（4） Look at the schematic diagram of the matrix keyboard ：4 individual IO Port control line ,4 individual IO Port control column .
/******************* How to judge input and output ********************/ P0 = 0xf0; // from IO output , write IO mouth
if(P0 != 0xf0) // from IO input , read IO mouth I/O Port is the general output port , hundred I/O The port can only be in and out 0 and 1,0 Corresponding to low level ,
1 Corresponding to high level , If it is 3.3V system , High level is 3.3, If 5V, The high level is 5V, Low level is 0V. If it's an output port , Is the MCU through the software to set the relevant register to let the
Port set high or low , Achieve the purpose of level output , If Dao Guo is used as the input port , It's a single chip The computer captures the specific level of the port and then sets the relevant registers , Then the software reads the data in the register 0 or 1, achieve
Input function . This is a very popular understanding ,
<>1.8.1 Matrix keyboard control idea
(1) Send it first （IO Pin out ）0x0f
(2) If there is a key to receive is not 0x0f, Data received from （IO Pin in ） Determine which line is pressed
(3) resend （IO Pin out ）0xf0
(4) Data received from （IO Pin in ） Determine which column is pressed
(5) comprehensive 2 Second row and column positions , Calculate the key value
<>1.8.12 Real combat of matrix keyboard
#include <reg51.h> // The matrix keyboard is used to press the key to display on the nixie tube in turn 0-F. /* connection ： Matrix keyboard ：P1 port Digital tube ： P0 port */
#define KEY P3 #define DIG P0 void delay10ms(void); unsigned char GetKey(void);
// Display of independent digital tube 0-F unsigned char varry[16] =
{0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,
0x80,0x90,0x88,0x83,0xc6,0xA1,0x86,0x8e}; unsigned char keynum = 0; void
main(void) { unsigned char Key = 0; while(1) { Key = GetKey(); if(Key != 0) {
DIG = varry[Key]; } } } void delay10ms(void) // error 0us { unsigned char a,b,c;
for(c=5;c>0;c--) for(b=4;b>0;b--) for(a=248;a>0;a--); } unsigned char
GetKey(void) { unsigned char KeyValue = 0; unsigned char hang = 0,lie = 0;
unsigned char flag = 0; KEY = 0x0f; if(KEY != 0x0f) { delay10ms(); switch (KEY)
{ case 0x0e: hang = 1; break; case 0x0d: hang = 2; break; case 0x0b: hang = 3;
break; case 0x07: hang = 4; break; default:break; } KEY = 0xf0; if(KEY != 0xf0)
{ switch (KEY) { case 0xe0: lie = 1; break; case 0xd0: lie = 2; break; case
0xb0: lie = 3; break; case 0x70: lie = 4; break; default:break; } KeyValue =
(hang - 1)*4 + lie; } return KeyValue; } return 0; }
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