8051 I/O Ports Structure

8051 I/O Ports Structure

AU : Dec.-08,15,16, May-14,18

The 8051 has 32 I/O pins configured as four eight-bit parallel ports (P0, Pl, P2 and P3). All four ports are bidirectional i.e. each pin will be configured as input or output (or both). All port-pins are multiplexed except the pins of port 1. Each port consists of a latch, an output driver and an input buffer.

Port 0 (Pins 32 - 39) : Port 0 pins can be used as I/O pins. The output drives and input buffers of port 0 are used to access external memory. Port 0 outputs the low order byte of the external memory address, time multiplexed with the data being written or read. Thus, port 0 can be used as a multiplexed address/data bus.

Port 1 (Pins 1 – 8) : Port 1 pins can be used only as I/O pins.

Port 2 (Pins 21 - 28) : The output drives of port 2 are used to access external memory. Port 2 outputs the high order byte of the external memory address when the address is 16 bits wide. Otherwise, port 2 is used as an I/O port.

Port 3 (Pins 10 - 17): All port pins of port 3 are multifunctional. Therefore, each pin of port 3 can be programmed to use as I/O or as one of the alternate function. They have special functions as shown below including two external interrupts, two counter inputs, two special data lines and two timing control strobes.

Review Questions

1. Explain the I/O ports of 8051. AU : Dec.-08, Marks 8

2. Explain the port operation in 8051 microcontroller. AU : May-14, Marks 16

3. Explain the I/O ports and their functions of 8051 microcontroller. AU : Dec.-15, Marks 16

4. Explain the I/O ports of 8051 microcontroller in detail. AU : Dec.-16, Marks 16

5. Briefly discuss the ports of 8051, internal circuits and its functions in detail. AU : May-18, Marks 13