Peripheral Interfacing( Intel 8086 CPU using PARALLEL PERIPHERAL INTERFACE (PPI-) 8255A, Slides of Microprocessor and Interfacing

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NEED FOR INTERFACING CHIPS

I/O devices are of different varieties, functions, features and specifications.  (^) The 8086 does not have the requisite hardware within it to manage each of them according to their special requirements and specifications. Thus I/O devices need some extra hardware to let them be interfaced to the processor. It is in this context that various interfacing chips have been designed. All these chips are programmable.

Specifications of the trainer

Fig 9.1 –A typical trainer kit

Figure 9.2 | The connections between an 8086,

8255 and three peripherals

• CHAPTER
• Figure 9.3 | Pin diagram of

Example 9.1-solution

Programming the PPI How is the chip programmed and what are the options available? Programming the chip involves only the writing of a particular word to the control register. The control register is an 8-bit register which can be written into. The bits of this word (called the control word) will decide the way the ports of the chip are to be configured.

Modes of Operation

The 8255 can be made to work in three modes as decided by the system designer. Mode 0: Basic input/output Mode 1: Strobed input/output Mode 2: Bi-directional bus

Mode 0

The specifications of this mode are: i) Two 8-bit ports and two 4-bit ports. ii) Any port can be input or output. iii) Outputs are latched iv) Inputs are not latched. v) 16 different input/output combinations possible.

Example 9.2-solution

Example 9. It is necessary to read the setting of 12 switches which are connected to the 8255 and display it on LEDs.  (^) Draw the setup and write the program for the same.