Microcontroller - internal resources, minimum system, hardware basics

1, microcontroller internal resources

STC89C52: 8KFLASH, 512 bytes RAM, 32 IO ports, 3 timers, 1 UART, 8 interrupt sources

(1) Flash (hard disk) - program storage space - erase 100,000 times, power data is not lost, read and write speed is slow

(2) RAM (memory) - data storage space - power loss data loss, read and write speed, unlimited use

(3) SFR - Special Function Registers

2、SCM minimum system

Minimum system: The minimum components make up the system that the microcontroller can work on.

Three elements:

(1) Power Supply Circuit: 5V

(2) Crystal oscillator circuit: 11.0592MHZ, two 30PF

(3) Reset circuit:

P0: Open drain output, pull-up resistor must be added

Quasi-bidirectional port:

Strong push-pull output: strong current drive capability

High impedance

Pull-up and pull-down resistors: The pull-up circuit pulls an indeterminate signal high through a resistor while limiting the current. The pull-down resistor is pulled down to low level.

Pull-up and pull-down resistor selection: Considered from the aspect of reducing power consumption should be large enough, because the greater the resistance, the smaller the current; drive capacity, small resistance

3, hardware basic knowledge

(1) Electromagnetic Interference (EMI) - Electrostatic Discharge (ESD), Fast Instantaneous Pulse (EFT), Surge (Surge)

(2) Use of decoupling capacitors

Low-frequency filter capacitors, the most commonly used tantalum capacitors, electrolytic capacitors, ceramic capacitors, remove the power supply low-frequency ripple, the role of stable power supply.

High-frequency filter capacitor, near the capacitor, usually 104 capacitors to remove high-frequency interference.

(3), Transistor (PNP, NPN) b, c, e --- Voltage Drive

Control application

Driver application

4, LED light-emitting diode - current drive

Usually red LED chip, driven by current, voltage 1.8V ~ 2.2V, current 1 ~ 20mA, brightness changes in 1 ~ 5mA, 5mA or more brightness is basically the same.

VCC voltage is 5V, LED from

The body pressure drop is about 2V, then the voltage on the right R34 resistor is 3V.

R = U/I - 1~20mA - R: 150~3K

5, C language basis

(1), basic operators

+ - * / % ++ -- = == != += -= << >> && || ! & | ~ ^

(2) Cycle (C language to represent a statement)

For/while/do...while

For (expression1; expression2; expression3)

{

Statement; // can be empty

}

While (expression) // expression is true, execute the statement

{

Statement; // can be empty

}

Do

{

Statement; // can be empty

}while (expression);

(3) Functions (modular thinking)

Type function name (parameter type parameter)

{

Function body

}

(4) Array

<1>, with the same data type

<2>, with the same type

<3>, continuous storage in memory

(5), 51 microcontroller commonly used delay method - cycle, timer

(P0 = ~(1 << i++);)

5, water lights

Give a low level to the IO port to light the LED lamp.

Note: The operation of the peripheral device by the SCM is actually the control of the IO port level.

#include // Header file containing special function register definitions

Typedef unsigned int uint;

Typedef unsigned char uchar;

Int main(void)

{

Uint i = 0; // Define loop variable i for software delay

Uchar j = 0; // Define count variable j for shift control

While(1) // main loop, the program executes the loop body statement in an infinite loop

{

P0 = ~(1 << j++); // P0 is equal to 1 left shift j bit, control 8 LEDs

For(i = 0; i < 20000; ++i); //Software delay

If(j >= 8) // After the shift count exceeds 7, it starts from 0 again

{

j = 0;

}

}

Return 0;

}