MCS-51 pin function description

　　MCS-51 is a standard 40-pin dual in-line integrated circuit chip

　　P0.0～P0.7: P0 port 8-bit bidirectional port line.

　　P1.0～P1.7: P1 port 8-bit bidirectional port line.

　　P2.0～P2.7: P2 port 8-bit bidirectional port line.

　　P3.0～P3.7: P3 port 8-bit bidirectional port line.

　　ALE: Address latch control signal. When the system is expanded, ALE is used to control the latching of the lower 8-bit address output by the P0 port to achieve isolation of the lower address and data. In addition, since ALE outputs a positive pulse at a fixed frequency of 1/6 of the crystal oscillator, it can be used as an external clock or external timing pulse.

　　PSEN: External program memory read strobe signal. When reading external ROM, PSEN is valid (low level) to realize the read operation of external ROM unit.

　　EA: access program storage control signal. When the signal is low, the read operation of the ROM is limited to the external program memory; when the signal is high, the read operation of the ROM starts from the internal program memory and can be extended to the external program memory.

　　RST: reset signal. When the input reset signal continues to be at a high level for more than two machine cycles, it is effective to complete the reset initialization operation of the microcontroller.

　　XTAL1 and XTAL2: external crystal lead terminals. When using the chip's internal clock, these two lead terminals are used to connect the external quartz crystal and trimmer capacitor; when using the external clock, these two lead terminals are used to connect the external clock pulse signal.

　　VSS: ground wire.

　　VCC: +5V power supply.

　　The above is the definition and simple function description of the 40 pins of the MCS-51 microcontroller chip. Readers can find the corresponding pins according to the training circuit and check the connection and use of each pin in the circuit.