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Interfacing

  • William Buchanan
Chapter
Part of the Macmillan Master Series book series (PMSC)

Abstract

There are two main methods of communicating external equipment, either they are mapped into the physical memory and given a real address on the address bus (memory mapped I/O) or they are mapped into a special area of input/output memory (isolated I/O). Figure 15.1 shows the two methods. Devices mapped into memory are accessed by reading or writing to the physical address. Isolated I/O provides ports which are gateways between the interface device and the processor. They are isolated from the system using a buffering system and are accessed by four machine code instructions. The IN instruction inputs a byte, or a word, and the OUT instruction outputs a byte, or a word. A Pascal compiler interprets the equivalent high-level functions and produces machine code which uses these instructions.
Figure 15.1

Memory mapping or isolated interfacing

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Copyright information

© William Buchanan 1998

Authors and Affiliations

  • William Buchanan
    • 1
  1. 1.Department of Electrical and Electronic EngineeringNapier UniversityEdinburghUK

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