Introduction to Bioinformatics - North South University

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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
• 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
                1111 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
 1100   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

				
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