Programmable Peripheral Interface (PPI) - 8255

Unit – IV

Chapter - 8

(a) Programmable Peripheral Interface (PPI) - 8255

Contents

8.1 Features of 8255A   ... Dec.-04, May-06,09  ... Marks 4

8.2 Pin Diagram

8.3 Block Diagram  ... May-06,09,13,14,18, ... Dec.-13,15,17,        Marks 13

8.4 Operation Modes ... May-04,07,08,17, 18, ... Dec.-04,09,11,13,17,19 ... Marks 16

8.5 Control Word Formats  ... May-04,18, ... Dec.-05,07,08,16,19 ... Marks 4

8.6  8255 Programming and Operation ... May-04,11, ... Dec.-12,  ... Marks 8

8.7 Interfacing 8255 in I/O Mapped I/O ... Dec.-10,      ... Marks 16

8.8 Parallel Communication between Two MP Kits using Mode 2 of 8255

8.9 Two Marks Questions with Answers

8.10 University Questions with Answers (Long Answered Questions)

Features of  8255A

AU : Dec.-04, May-06,09

1. The 8255A is a widely used, programmable, parallel I/O device.

2. It can be programmed to transfer data under various conditions, from simple I/O to interrupt I/O.

3. It is compatible with all Intel and most other microprocessors.

4. It is completely TTL compatible.

5. It has three 8-bit ports (24 I/O pins) : Port A, Port B, and Port C, which are arranged in two groups of 12 pins. Each port has an unique address, and data can be read from or written to a port. In addition to the address assigned to the three ports, another address is assigned to the control register into which control words are written for programming the 8255 to operate in various modes.

6. Its bit set/reset mode allows setting and resetting of individual bits of Port C.

7. The 8255 can operate in 3 I/O modes :

Mode 0 : Simple Input/Output

Mode 1 : Input/Output with handshake

Mode 2 : Bi-directional I/O data transfer

a) In Mode 0, Port A and Port B can be configured as simple 8-bit input or output ports without handshaking. The two halves of Port C can be programmed separately as 4-bit input or output ports.

b) In Mode 1, two groups each of 12 pins are formed. Group A consists of Port A and the upper half of Port C while Group B consists of Port B and the lower half of Port C. Ports A and B can be programmed as 8-bit Input or Output ports with three lines of Port C in each group used for handshaking.

c) In Mode 2, only Port A can be used as a bidirectional port. The handshaking signals are provided on five lines of Port C (PC3 - PC7). Port B can be used in Mode 0 or in Mode 1.

8. All I/O pins of 8255 has 2.5 mA DC driving capacity (i.e. sourcing current of 2.5 mA).

Review Questions

1. What is known as PPI, what is the use of interfacing the same 8085?

2. List the features of 8255.