I/O Ports - 8051 Micro Controller

I/O Ports

ü The 8051 contains four I/O ports

ü All four ports are bidirectional

ü Each port has SFR (Special Function Registers P0 through P3) which works like a latch, an output driver and an input buffer

ü Both output driver and input buffer of Port 0 and output driver of Port 2 are used for accessing external memory

ü Accessing external memory works like this

1.     Port 0 outputs the low byte of external memory address (which is time- multiplexed with the byte being written or read)

2.     Port 2 outputs the high byte (only needed when the address is 16 bits wide)

ü Port 3 pins are multifunctional

ü The alternate functions are activated with the 1 written in the corresponding bit in the port SFR

Table 4.3 Alternate Functions of Port 3 pins

Serial Communication

Some of the external I/0 devices receive only the serial data. Normally serial communication is used in the Multi-Processor environment.8051 has two pins for serial communication.

ü SID- Serial Input data.

ü SOD-Serial Output data.

Interrupt Structure

ü The 8051 provides 4 interrupt sources

ü Two external interrupts

ü Two timer interrupts

Port Structure

ü The 8051 contains four I/O ports

ü All four ports are bidirectional

ü Each port has SFR (Special Function Registers P0 through P3) which works like a latch, an output driver and an input buffer

ü Both output driver and input buffer of Port 0 and output driver of Port 2 are used for accessing external memory

ü Accessing external memory works like this

ü Port 0 outputs the low byte of external memory address (which is time- multiplexed with the byte being written or read)

ü Port 2 outputs the high byte (only needed when the address is 16 bits wide)

ü Port 3 pins are multifunctional