MCU Learning Notes 51 MCU Basics

Compatible with MCS-51 are
Atmel's AT89C5X, which is discontinued and does not support ISP download. It has been replaced by AT89S5X, which can be ISP downloaded.
SST's SST89E5X, which comes with a monitoring program and can be simply simulated.
Hongjing STC (mainland) STC89C5X supports serial port downloads

STC89C52

1.          

AT indicates Atmel chip 
9 indicates flash memory
S indicates downloadable flash
LV indicates low voltage 3.3V
52 is model 2 indicates 8K ROM 
24 indicates maximum crystal oscillator 24M
P indicates dual in-line package D indicates ceramic package J indicates square package S, Q indicates surface mount package
C indicates commercial products 0~75 degrees I indicates industrial products, high point of temperature range A indicates automotive products M indicates military grade U indicates lead-free products

51 Internal structure 
        8-bit CPU 4KROM 128 bytes of RAM 4 8-bit IO ports 1 full-duplex serial port 2 16-bit timers and counters 5 interrupt sources
 

RAM is equivalent to memory. It is lost when power is off. It is used to store computing data.

ROM is equivalent to a hard disk. It is used to store programs and is not lost when power is off.

 

There are only two levels in digital circuits: high +5V and low 0V.
        RS232 level: computer serial port high -12V and low +12V. So the single-chip microcomputer and computer communication need to convert the level.




The MCS-51 series of single-chip microcomputer products include 8051, 8031, 8751, 80C51, 80C31 and other models (the first three are CMOS chips, and the last two are CHMOS chips). Their structures are basically the same, and their main difference is reflected in the configuration of the memory. The 8051 has a 4K-byte mask ROM program memory inside, the 8031 ​​has no program memory inside, and the 8751 replaces the ROM inside the 8051 with an EPROM. The 89C51 produced by ATMEL changed the EPROM into a 4K flash memory.　　 

The MCS-51 microcontroller is a chip that integrates the basic functional components required for a computer, such as CPU, RAM, ROM, timer/counter, and I/O lines with multiple functions. The MCS-51 microcontroller contains the following components:

◆ An 8-bit CPU;
　　◆ An on-chip oscillator and clock circuit;
　　◆ 4K bytes of ROM program memory;
　　◆ 128 bytes of RAM data memory;
　　◆ Two 16-bit timers/counters;
　　◆ Control circuits that can address 64KB external data memory and 64BK external program memory space;
　　◆ 32 programmable I/O lines (four 8-bit parallel I/O ports);
　　◆ A programmable full-duplex serial port;
　　◆ With five interrupt sources and two priority nested interrupt structures.

Internal structure of MCS-51 microcontroller

 

MCS-51 microcontroller pin functions:

 

MCS-51 MCU pin diagram

1 Power supply line:
　　VCC: +5 V power supply. VSS: ground line. 

2 RST: Reset signal line.
　　When the input reset signal continues to be high for more than two machine cycles, it is valid and is used to complete the reset initialization operation of the microcontroller.

　　3 Signal pin introduction 
              P0.0 ~ P0.7: P0 port 8-bit bidirectional line. 
              P1.0 ~ P1.7: P1 port 8-bit bidirectional line. 
              P2.0 ~ P2.7: P2 port 8-bit bidirectional line. 
              P3.0 ~ P3.7: P3 port 8-bit bidirectional line.

4 XTAL1 and XTAL2: external crystal pins

5 control lines:
　　(1) ALE/PROG
    (2) EA/VPP
　　(3) PSEN