[MCU] 2.2 pin function of AT89S52

2.2 AT89S52 Pin function of

• AT89S52 With all kinds of 8051 The pins of MCU are compatible . at present ,AT89S52 Single chip microcomputer mostly adopts 40 Pin DIP encapsulation （ Double in line ）, as well as 44 Pin PLCC and TQFP Chip with packaging method .
  
  
• 44 Pin PLCC and TQFP Chip with packaging method , Yes 4 Only pins are useless , Marked as “NC”.
  
  
  The pins can be divided into the following according to their functions 3 class ：

• （1） Power supply and clock pin —VCC、VSS;XTAL1、XTAL2.
• （2） Control pin — PSEN*、ALE/PROG*、EA* /VPP、RST
• （3）I/O Port pin ——P0、P1、P2、P3, by 4 individual 8 position I/O mouth
  
  
  The following describes the functions of each pin .

2.2.1 Power supply and clock pin

1. Power pin
   • VCC（40 foot ）：+5V Power Supply .
   • VSS（20 foot ）： Digitally .
     
2. Clock pin
   • XTAL1（19 foot ）： On chip oscillator inverting amplifier and clock generator circuit input . use On chip oscillator when , This pin is connected to the outside Quartz crystal and fine tuning capacitor . External clock source , This pin is connected External clock oscillator The signal of .
   • XTAL2（18 foot ）： The output of the on-chip oscillator inverting amplifier . When using On chip oscillator , This pin is connected to the outside Quartz crystal and fine tuning capacitor . When using External clock source when , Benjiao In the air .
     
     

2.2.2 Control pin

（1）RST (RESET,9 foot )

• Reset signal input , Add The duration is greater than 2 High level of a machine cycle , It can reset the single chip microcomputer . Normal work , This pin level should ≤ 0.5V.
• When the watchdog timer overflows the output , This pin will output up to 96 High level of clock oscillation cycle .

（2） EA* / VPP (Enable Address/Voltage Pulse of Programing,31 foot )

• EA*： Pin The first function ： External program memory access allows the control side to .
  

• EA* = 1, stay PC The value does not exceed 1FFFH（ That is, not beyond the film 8KB Flash Address range of memory ） when , Single chip microcomputer reading On chip program memory （8KB） Program in , but PC It's worth more than 1FFFH （ That is, beyond the film 8KB Flash Address range ） when , take Automatic steering reading sheet out （2000H-FFFFH） A program in a program memory space .
• EA* = 0, Read only external program memory The content in , The address range read is 0000H～FFFFH, Intraslice 4KB Flash Program memory does not work .
  

• VPP： Pin Second function , On film Flash Programming , Pick up Programming voltage .
  
  

（3）ALE / PROG*（Address Latch Enable/PROGramming,30 foot ）

• ALE by Address latch control signal end , by The first function . Due to the limited number of pins ,P0 The mouth is as low 8 Bit address bus and 8 Bit data bus Time division multiplexing Of . When MCU accesses external program memory or external data memory ,ALE The negative jump of will be single-chip P0 Mouth first low 8 Bit address lock exists P0 In the address latch connected outside the port , then P0 Mouth again as 8 Bit data bus use , Pictured 2-4 Shown .
  
  • Besides , Single chip microcomputer The normal operation when ,ALE End There is always a positive pulse signal output , This frequency is the clock frequency fosc Of 1/6. It can be used as external timing or trigger signal .
  • Be careful , whenever AT89S52 External access RAM when （ perform MOVX Class instructions ）, want Lose one ALE pulse .
    If not required ALE End output pulse signal , Can be special function register AUXR（ The address is 8EH, Will be introduced later ） Of The first 0 position （ALE Forbidden bit ） Set up 1, To prohibit ALE operation , But execute instructions to access external program memory or external data memory “MOVC” or “MOVX” when ,ALE Still valid . namely ALE The forbidden bit does not affect access to external memory .
• PROG*： Pin Second function , On film Flash Programming , by Program the pulse input pin .

（4） PSEN* （Program Strobe ENable,29 foot ）

• Off chip program memory read strobe signal , Low level active .

2.2.3 parallel I/O Port pin

（1）P0 mouth ：P0.7～P0.0 Pin

• Open drain 8 Bit parallel two-way I/O mouth . As an output port , Each pin can drive 8 individual LS type TTL load . When AT89S52 Expand external memory and I/O Interface chip ,**P0 The port is low for time-sharing multiplexing 8 Bit address / data bus .** In the P0 Write in “1” Then it becomes the input port of high resistance state .
• When P0 To act as Universal I/O mouth When using , A pull-up resistor is required , This is Quasi two-way port .
• In the face of Flash When programming program memory ,P0 Port receives byte code , Program verification P0 Port output byte code , During the program verification, the pull-up resistor should be connected externally .

（2）P1 mouth ：P1.7～P1.0 Pin

• Quasi bidirectional I/O mouth , have Internal pull-up resistor , Can drive 4 individual LS type TTL load .

• In the opposite film Flash It is defined as low 8 Bit address line .

• P1 The second function of some pins of the port is as follows .

  • P1.0/T2：T2 Feet are timers T2 External counting signal input of T2.
  • P1.1/T2EX：T2EX by T2 The capture of / Reload trigger and direction control T2EX.
  • P1.5/MOSI：MOSI Used for on-chip Flash Memory serial programming and verification .
  • P1.6/MISO：MISO Used for on-chip Flash Memory serial programming and verification .
  • P1.7/SCK：SCK Used for on-chip Flash Shift pulse input pin for serial programming and verification of memory .

• Be careful ：AT89S51 And AT89S52 The difference in pins is only 1 foot （P1.0） And 2 foot （P1.1） On ,AT89S52 Of 1 foot （P1.0） And 2 foot （P1.1） , respectively, Added timer / Counter T2 Two external pins of T2 and T2EX The reuse function of . When AT89S52 SCM does not use on-chip T2 The two pins of T2（P1.0） and T2EX（P1.1） The reuse function of ,AT89S51 As well as a variety of 8051 Compatible with AT89S52 The pin function of is exactly the same , Their peripheral hardware interface circuits are completely universal .

• But if you use a timer T2 External count input of T2（P1.0） and “ capture ” Input T2EX （P1.1） The function of the , be AT89S52 Of P1.0 Feet and P1.1 Feet can't be used for general purpose I/O Use , This is a AT89S52 And AT89S51（ or AT89C51） Minor differences in peripheral interface circuit design .

（3）P2 mouth ：P2.7～P2.0 Pin

• Quasi bidirectional I/O mouth , Pin There is a pull-up resistor inside , Can drive 4 individual LS type TTL load .
• When AT89S52 Access external memory and I/O When you talk ,P2 mouth As high 8 Bit address bus use , High output 8 Bit address .
• When P2 Mouth not as high 8 Bit address bus , Can be used as General purpose I/O mouth Use .

（4）P3 mouth ：P3.7～P3.0

• Quasi bidirectional I/O mouth , have Internal pull-up resistor .
• P3 Oral The first function As a General purpose I/O mouth Use , Can drive 4 individual LS type TTL load .
• P3 Mouth can also provide Second function . The second function is defined in table 2-1, Remember .
  
• in summary ,P0 mouth It can be used as a bus port , It is a two-way port . As a universal I/O When using mouth , Subject to two-way opening , At this time, the pull resistance should be added .P1 mouth 、P2 mouth 、P3 mouth Both are quasi two-way ports .
  
  
• Be careful ： The difference between quasi two-way port and two-way port . The quasi two-way port has only two states . and P0 The port is used as a bus , There is no pull-up resistance in the port line , At high resistance “ suspension ” state . so P0 The mouth is bidirectional Tristate I/O mouth .
• Why? P0 The mouth should have high resistance “ suspension ” state ？ Quasi bidirectional I/O The mouth has no high resistance “ suspension ” state .
• in addition , Quasi two-way port For general use I/O When using the input port of , Be sure to write to this port first “1” . The difference between the above quasi two-way port and two-way port , The reader is reading 2.5 Postganglionic , Will have a deep understanding .
  
  
• thus ,40 Pins have been introduced , Remember that the function of each pin is very important for the hardware circuit design of the application system .