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  1. I/O devices have 16 bit addresses
  2. I/O devices are accessed during IN and OUT instructions
  3. There can be a maximum of 256 input and 256 output devices
  4. Logic operations cannot be performed
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1 Answers

Option 1 : I/O devices have 16 bit addresses

Microprocessors normally use two methods to connect external devices:

  • Memory-mapped I/O
  • Port/Peripheral Mapped I/O

Memory-Mapped I/O:

  • 16-bit device address
  • Data transfer between any general-purpose register and I/O port
  • The memory map (64K) is shared between the I/O device and system memory
  • More hardware is required to decode 16-bit address
  • Arithmetic or logic operation can be directly performed with I/O data

Memory-mapped I/O is mapped into the same address space as program memory and/or user memory and is accessed in the same way. Port mapped I/O uses a separate, dedicated address space and is accessed via a dedicated set of microprocessor instructions.

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Peripheral Mapped I/O:

  • 8-bit device address
  • Data is transferred only between the accumulator and I.O port
  • The I/O map is independent of the memory map; 256 input device and 256; The output device can be connected
  • Less hardware is required to decode 8-bit address
  • Arithmetic or logical operation cannot be directly performed with I/O data
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