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

INS Instructions INSB – Input String Byte, from I/O device to memory location Table 4-14: From Brey’s Book

Example 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 OUTSB – Output String Byte, from string memory location to I/O device Table 4-15: From Brey’s Book

Example 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 Decode 8-bit I/O ports F0H – F7H using 74ALS138 decoder 0000 = F0H 1111 0111 = F7H

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) 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? I/O Devices

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 82C55 Draw the diagram for interfacing 82C55 for the following addresses 8C (Port A), 9C (Port B), AC (Port C) and BC (command register). CBA 011

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