IO Interfacing- Free Microprocesor notes

I/O STRUCTURE OF A TYPICAL MICROCOMPUTER:

There are three major types of data transfer between the microcomputer and art I/O device. They are,

Programmed I/O : In programmed I/O the data transfer is accomplished through an I/O port and controlled by software.
Interrupt driven I/O : In interrupt driven I/O, the I/O device will interrupt the processor, and initiate data transfer.
Direct memory access (DMA) : In DMA, the data transfer between memory and I/O can be performed by bypassing the microprocessor.

INTERFACING I/O AND PERIPHERAL DEVICES:

1. For data transfer from input device to processor the following operations are performed.

The input device will load the data to the port.
When the port receives a data, it sends message to the processor to read the data.
The processor will read the data from the port.
After a data have been read by the processor the input device will load the next data into the port.

2. For data transfer from processor to output device the following operations are performed.

The processor will load the data to the port.
The port will send a message to the output device to read the data.
The output device will read the data from the port.
After the data have been read by the output device the processor can load the next data to the port.
The various INTEL 110 port devices are 8212, 8155/8156, 8255, 8355 and 8755.
8212
The 8212 is a 24 pin IC.
It consists of eight number of D-type latches.
It has 8-input lines DI1 to DI8 and 8-output lines DO1 to DO8
The 8212 can be used as an input or output device
It has two selecting device DS1 (low) and DS2.

If,

8155:

8156:

8255:

It has 3 numbers of 8-bit parallel I/O ports (port A, B and C).
Port-A can be programmed in mode-0 mode-1 or mode-2 as input or output port.
Port-B can be programmed in mode-1 and mode-2 as 1/Oport.
When ports A and B are in mode-0, the port-C can be used as I/O port.
One logic low chip select (CS) pin.
It requires four internal addresses