MICROPROCESSOR 8085 AND ITS INTERFACING

MICROPROCESSOR 8085 AND ITS INTERFACING

Microprocessor based system design involves interfacing of the processor with one or more peripheral devices for the purpose of communication with various input and output devices connected to it.  During the early days of the microprocessor revolution, these techniques required complex hardware consisting of Medium scale integration devices making the design highly complex and time consuming.  So, the manufacturers (INTEL) have developed a large number of general and special purpose peripheral devices most of them being single chip circuits.  They are also programmable devices.  Hence these peripheral devices are found to be of tremendous use to a system designer.

Peripheral devices, can broadly be classified into two categories.

(a)  General purpose peripherals and

(b)  Special purpose peripherals (Dedicated function peripherals)

General purpose peripherals are devices that perform a task but may be used for interfacing a variety of I/O devices to microprocessor.  The general purpose devices are given below:

·         Simple I/O                                                     --           (Non-programmable)

·         Programmable peripheral Interface (PPI)       –          (8255)

·         Programmable Interrupt Controller                 –          (8259)

·         Programmable DMA Controller                     –          (8257)

·         Programmable Communication Interface       –          (8251)

·         Programmable Interval Timer                          –          (8253/8254)
       Programmable keyboard interface                  -- 8279

Special function peripherals are devices that may be used for interfacing a microprocessor to a specific type of I/O device.  These peripherals are more complex and therefore, relatively more expensive than general purpose peripherals.  The special function peripherals (Dedicated function peripherals)

  Programmable CRT Controller

·                                 Programmable Floppy Disc Controller

·                                 Programmable Hard Disc Controller

·                                 Programmable Keyboard and display interface.

The functioning of these devices varies depending on the type of I/O device they are controlling.