单片机毕业设计外文文献翻译

英文原文：

80C51

8051 single-chip micro-computer, referred to as microcontrollers, there are known as micro-controller, a micro-computer re -

To branch. SCM is developed in the mid 70s a large-scale integrated circuit chip, a CPU, RAM, ROM, I / O interfaces and interrupt system on the same silicon device. Since the 80s, Microcontroller rapid development, all kinds of new products are constantly emerging, there have been many high-performance of new models now become the field of factory automation and control of the pillar industries.

Pin Function:

MCS-51 is a standard 40-pin DIP IC chip, pin distribution ---- microcontroller pin diagram please refer to:

P0.0 ~ P0.7 P0 port 8-bit bidirectional port lines (in the pin 39 to No. 32 terminal). P1.0 ~ P1.7 P1 port 8-bit bidirectional port line (pin 1 in the No. 8 terminal).

P2.0 ~ P2.7 P2 port 8-bit bidirectional port lines (in the pin terminal 21 ~ 28).

P3.0 ~ P3.7 P3 port 8-bit bidirectional port lines (in the pin terminal 10 ~ 17).

This four I / O port has not exactly the same function, we can get to learn, and other books though, but written in too deep, difficult to understand for beginners, here are according to my own expression to write the I believe that you can understand.

P0 port has three functions:

1, external expansion memory, as the data bus (Figure 1 in D0 ~ D7 of data bus interface)

2, external expansion memory, as the address bus (Figure 1 in A0 ~ A7 to address bus interface)

3, is not extended, it can do a general I / O to use, but within the supreme pull-up resistor, as an input or output should be connected to an external pull-up resistor.

P1 port Zhizuo I / O port to use: its internal pull-up resistor.

P2 port has two functions:

1,An extended external memory when used as an address bus

2, doing a general I / O port used, and their internal pull-up resistor;

P3 port has two functions:

As well as I / O using the external (the internal pull-up resistor), there are some special features, from a special register to set the specific features please refer to our explanation behind the pin.

Internal EPROM of the microcontroller chip (for example, 8751), for the writing process required to provide specialized programming and programming pulse power, these signals are also provided in the form from the signal pin, and Namely: programming pulse: 30 feet (ALE / PROG)

Programming voltage (25V): 31 feet (EA / Vpp)

In introducing the four I / O port referred to a "pull-up resistor" Then, pull-up resistor is what Dongdong do? What role does he play? Said the resistance that is of course, is a resistor, when as an input, the pull-up resistor pulled its potential, if the input is low you can provide a current source; Therefore, if the P0 port as long as the input, in the high impedance state, only an external pull-up resistor to be effective. ALE / PROG address latch control signal: in a system is extended, ALE is used to control the P0 port output low 8-bit address latch latch get together in order to achieve low address and data segregation. (In the back on the expansion of the curriculum, we will see the 8051 expansion of EEPROM circuit, the ALE and the 74LS373 in Figure G-latches connected to the external CPU to access when the time to lock the address low address, the P0 port output. ALE may be high may also be low, when the ALE is high, allowing address latch signal when accessing external memory, ALE signals a negative transition (from positive to negative) P0 port on the lower eight address signals into the latch. when ALE is low, when, P0 port on the content and the output latch line. on the latch, and we will be introduced later.

In the absence of access to external memory during the period, ALE 1 / 6 oscillator frequency output cycle (ie, frequency of 6 points), when access to external memory to 1 / 12 oscillator cycle, the output (12 min frequency). From here we can see that when the system does not extend when the ALE will be 1 / 6 cycle, fixed frequency oscillator output, so can be used as an external clock, or the use of an external timing pulse.

PORG pulse input for the program: In the fifth lesson MCU's internal structure and composition, we know that in 8051 within the a 4KB or 8KB of program memory (ROM), ROM's role is to be used to store user needs implementation of the program, then we are into how to write good programs into this ROM in it? Is actually programmed into the pulse input can be written, this pulse input port is PROG. PSEN external program memory read strobe: In reading an external ROM, PSEN low effective, in order to achieve an external ROM module read.

1, the internal ROM reading, PSEN is not action;

2, external ROM reading at each machine cycle will move twice;

3, external RAM read, the two PSEN pulse is skipped will not be output;

4, external ROM, and ROM-foot-phase OE.

See Figure 2 - (8051 extension 2KB EEPROM circuit in Figure PSEN and expansion ROM in the OE pin-phase)

EA / VPP access and sequence memory control signals

1, then high time:

CPU reads the internal program memory (ROM)

Expansion of the external ROM: When reading the internal program memory than

0FFFH (8051) 1FFFH (8052) automatically reads the external ROM.

2, then low when: CPU to read external program memory (ROM). In the previous study, we are aware, there is no internal ROM MCU 8031, then 8031 microcontroller in the application, this pin is a low level of direct.

3,8751 Shaoxie internal EPROM, to make use of this pin input voltage of 21V for