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Difference between Memory Mapped IO and IO Mapped IO with reference to 8085 microprocessor

  • Last Updated : 03 Dec, 2020

The microprocessor cannot do anything by itself therefore, It needs to be linked with memory, extra peripherals, or IO devices. This linking is called Interfacing.

The interfacing of the I/O devices in 8085 can be done in two ways :

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1. Memory-Mapped I/O Interfacing :
In this kind of interfacing, we assign a memory address that can be used in the same manner as we use a normal memory location.



2. I/O Mapped I/O Interfacing :
A kind of interfacing in which we assign an 8-bit address value to the input/output devices which can be accessed using IN and OUT instruction is called I/O Mapped I/O Interfacing.



Difference between Memory-Mapped I/O Interfacing and I/O Mapped I/O Interfacing :

FeaturesMemory Mapped IOIO Mapped IO
AddressingIO devices are accessed like any other memory location.They cannot be accessed like any other memory location.
Address SizeThey are assigned with 16-bit address values.They are assigned with 8-bit address values.
Instructions UsedThe instruction used are LDA and STA, etc.The instruction used are IN and OUT.
CyclesCycles involved during operation are Memory Read, Memory Write.Cycles involved during operation are IO read and IO writes in the case of IO Mapped IO.
Registers CommunicatingAny register can communicate with the IO device in case of Memory Mapped IO.Only Accumulator can communicate with IO devices in case of IO Mapped IO.
Space Involved216 IO ports are possible to be used for interfacing in case of Memory Mapped IO.Only 256 I/O ports are available for interfacing in case of IO Mapped IO.
IO/M` signalDuring writing or read cycles (IO/M` = 0 ) in case of Memory Mapped IO.During writing or read cycles (IO/M` = 1) in case of IO Mapped IO.
Control SignalNo separate control signal required since we have unified memory space in the case of Memory Mapped IO.Special control signals are used in the case of IO Mapped IO.
Arithmetic and Logical operationsArithmetic and logical operations are performed directly on the data in the case of Memory Mapped IO.Arithmetic and logical operations cannot be performed directly on the data in the case of IO Mapped IO.

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