【51 MCU】Summary of basic knowledge of the exam (pins)

Examination scope:

• Optional reading book after-class exercises

• Main question:

1. Pure programming: In the first four experiments, multiplication is not tested.

2. Interrupt, timer T1: square wave book example 5-1, can also be implemented in C language

3. Display, keyboard: 8-bit/16-bit (independent/matrix keyboard, Scanner)

4. 0832/0809 Example 10-1 (1) (2) (3) 10-6, 10-6 above program (square wave, rectangular wave)

5. Chapter 8, Expansion Chart, "Just know how to do the content of Lecture 14"

Serial Port:

• AFTER:

• When the external memory is expanded, it is used as the data bus, DB

• When not expanded, it can be used as a general I/O, but there is no internal pull-up resistor. When used as input or output, an external pull-up resistor should be connected.

• P1 port:

• Only used as I/O port: it has a pull-up resistor inside.

• The P2 port has two functions:

• When expanding external memory, it is used as an address bus, AB

• Used as a general I/O port, it has a pull-up resistor inside;

• The P3 port has two functions:

• In addition to being used as IO,

• There are also some special functions, which are set by special registers (RXD, TXD, external interrupt input INT1/0, WR, RD)

• RST: Reset terminal. (2Ts reset, power-on reset, key pulse reset, key level reset)

• XTAL1, XTAL2: Clock input, external crystal oscillator circuit or pulse circuit

• ALE: low 8 bits, data

• EA：ROM，

• EA is invalid: first access the chip, then access the chip, then cannot add more than 64KB of external expansion

• EA effective: direct access to external ROM

• EA must enable interrupts when it is interrupted

• PSEN

• When reading external program memory (EA is valid), _PSEN_ low level is effective to enable the external ROM to run.

• EX0/EX1: External interrupt enable signal

• IT0, IT1: Interrupt mode: 1 is falling edge trigger, 0 is low level trigger, the default is low level trigger

Tips：

1. The serial port can be used as an I/O port: P0 is an external pull-up resistor; P1, 2, and 3 have internal pull-up resistors.

2. Pins involving external RAM and ROM

3. Time-division multiplexing:

English explanation:

1. cy = cycle

2. osc = oscillating (cycle)

3. External: The X in XTAL stands for external

4. sbit is used to store bit-addressable objects

5. ALE==Address Lock Enable

Crystal Oscillator

• 51 Minimum system:

• Power supply, ground, reset circuit, crystal oscillator circuit.

• Crystal Oscillator:

• It provides the pulse of the complex timing circuit of 51 single-chip microcomputer, and is the heart of 51 single-chip microcomputer! The two pins XAL1 and XAL2 are the clock access pins, which are the arteries of 51. The oscillation generated by the crystal oscillator is input into the single-chip microcomputer, and there are pulse signals one by one, and the timing circuit inside 51 can work. These pulses are called clock signals, the period of the clock signal is called the clock period, and the frequency is called the clock frequency.