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Lecture 13 Basic I/O Interface. Presented By Dr. Shazzad Hosain Asst. Prof. EECS, NSU. I/O Port Address Decoding. I/O port address decoding is very similar to address decoding Any I/O device is addressed by a port number

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Lecture 13 basic i o interface

Lecture 13Basic I/O Interface

Presented By

Dr. ShazzadHosain

Asst. Prof. EECS, NSU

I o port address decoding
I/O Port Address Decoding

  • I/O port address decoding is very similar to address decoding

  • Any I/O device is addressed by a port number

  • Reading or writing to an I/O device is to read or write to that port address

Ins instructions
INS Instructions

  • INSB – Input String Byte, from I/O device to memory location

Table 4-14: From Brey’s Book


  • Read 50 bytes of data from an I/O device whose address in 03ACH and store the data in LISTS array

Example 4-7: From Brey’s Book

Outs instructions
OUTS Instructions

  • OUTSB – Output String Byte, from string memory location to I/O device

Table 4-15: From Brey’s Book


  • Transfer data form memory array (ARRAY) to an I/O device at I/O address 3ACH

Example 4-8: From Brey’s Book

Decoding 8 bit i o addresses
Decoding 8-Bit I/O Addresses

  • Decode 8-bit I/O ports F0H – F7H using 74ALS138 decoder

0000 = F0H

1111 0111 = F7H

Decoding 8 bit i o addresses1
Decoding 8-Bit I/O Addresses

  • Develop an I/O port decoder, using a 74ALS138, for the 8-bit I/O port addresses 10H, 12H, 14H, 16H, 18H, 1AH, 1CH and 1EH

The programmable peripheral interface ppi
The Programmable Peripheral Interface (PPI)

  • 82C55 is a very popular low-cost interfacing component found in many applications

  • It sits between microprocessor and the I/O devices

  • It has three ports

    • Port A

    • Port B

    • Port C

  • Also has an internal command register

Why peripheral
Why Peripheral?

I/O Devices

Interfacing 82c55
Interfacing 82C55

  • Connect 82C55 so that it functions at 8-bit I/O port addresses C0H (port A), C2H (port B), C4H (port C), and C6H (command register).

1100 0000 = C0H

0010 = C2H

1100 0100 = C4H

1100 0110 = C6H

Interfacing 82c551
Interfacing 82C55

  • Draw the diagram for interfacing 82C55 for the following addresses 8C (Port A), 9C

  • (Port B), AC (Port C) and BC (command register).




  • Chapter 9 The Intel Microprocessors – by Barry B. Brey