Question: How many I/O lines are there in the pins of the MCS-51 series microcontrollers? What is the relationship between them and the address bus and data bus of the microcontroller? How many bits are there in the address bus and data bus? How big is the address space that can be addressed externally?
Answer: The 80C51 microcontroller has 4 I/O ports, each of which is an 8-bit bidirectional port, occupying a total of 32 pins. Each port includes a latch (i.e., special registers P0 to P3), an input driver, and an input buffer. The four ports are usually called P0 to P3. In a system without external memory expansion, each of these four ports can be used as a bidirectional general I/O port. In a system with external memory expansion, port P2 is used as the high 8-bit address line, and port P0 is used as the low 8-bit address line and bidirectional data bus in a time-sharing manner.
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