The 4 I/O ports of the 8051 single-chip microcomputer are basically the same in structure, but each has its own characteristics. These four ports are all 8-bit bidirectional ports, and each port includes a latch, an output driver and an input buffer. In a system without external expansion memory, each of these four ports can be used as a bidirectional general I/O port. When used as a general general purpose I/O input, it is necessary to write "1" to the latch first to make the output drive field effect tube FET cut off, so as to avoid misreading the data. Their characteristics are as follows:
(1) Port P0 is a bidirectional 8-bit tri-state I/O port. It can be used as a general-purpose I/O port, as well as a data bus for external expansion and a time-sharing multiplex port for the lower 8-bit address bus. When used as a general I/O port, the output data can be latched without an external special latch; the input data can be buffered, which increases the reliability of data input. Each pin can drive 8 TTL loads.
(2) Port P1 is an 8-bit quasi-bidirectional I/O port with pull-up resistors inside. It is generally used as a general-purpose I/O port. Each bit of it can be defined as an input line or an output line. When used as an input, The latch must be set to 1. Each pin can drive 4 TTL loads.
(3) Port P2 is an 8-bit quasi-bidirectional I/O port with internal pull-up resistors, which can be directly connected to external I/O devices. It is multiplexed with the upper 8 bits of the address bus and can drive 4 TTL loads. Generally used as the high 8-bit address bus for external expansion.
(4) Port P3 is an 8-bit quasi-bidirectional I/O port with a pull-up resistor inside. It is a dual-function multiplex port, and each pin can drive 4 TTL loads. When used as a general I/O port, the function is the same as the P1 port, and the second function is commonly used. When used as the second function, please refer to the other content of this site (SCM Home) for your role.
Other capacitors
Other Capacitors,Ac Filter Capacitor,Power Saver Capacitor,Line Filter Capacitor,Low Voltage Capacitor
YANGZHOU POSITIONING TECH CO., LTD. , https://www.pst-thyristor.com