Memory Mapped I/O and I/O Mapped I/O March

 Memory Mapped I/O and I/O Mapped I/O March 

Table: Comparison between Memory Mapped I/O and I/O Mapped I/O

S.No
Memory Mapped I/O
S.No
I/O Mapped I/O
1
Address width is 16-bit. A0 to A15 are used to generate address of the device.
1
Address width is 8-bit. A0 to A15 lines are used to generate address of the device.
2
MEMR and MEMW control signals are used to control read and write I/O operations respectively.
2
IOR and IOW control signals are used to control read and write I/O operations respectively.
3
Instructions available are STA addr, LDA addr, LDAX rp, STAX rp, ADD M, CMP M, MOV r, M, etc.
3
IN and OUT are the only available instructions.
4
Data transfer takes place between any register and I/O device.
4
Data transfer takes place between accumulator and I/O device.
5
Maximum number of I/O devices that can be addressed is 65536 (theoretically).
5
Maximum number of I/O devices that can be addressed is 256.
6
Execution speed using STA addr, LDA addr is 13 T-state and for MOV M, r, etc., it is 7-T states.
6
Execution speed is 10 T-states.
7
Decoding 16-bit address will require more hardware circuitry.
7
Decoding 8-bit address will require less hardware circuitry.

OR

S. No
Characteristics
Memory-Mapped I/O
Peripheral I/O
1
Device address
16-bit
8-bit
2
Control signals for Input/Output
MEMR/MEMW
IOR/IOW
3
Instructions available
Memory-related instructions such as STA; LDA; LDAX; STAX; MOV M,R; ADD M; SUB M; ANA M; etc.
IN and OUT
4
Data transfer
Between any register and I/O
Only between I/O and the accumulator
5
Maximum number of I/Os possible
The memory map (64K) is shared between I/Os and system memory.
The I/O map is independent of the memory map; 256 input device and 256 output device can be connected
6
Execution Speed
13 T-states (STA, LDA) 7 T-states (MOV M,R)
10 T-states
7
Hardware requirements
More hardware is needed to decode 16-bit address
Less hardware is needed to decode 8-bit address
8
Other feature
Arithmetic or logical operations can be directly performed with I/O data
Not available

REFERENCES



  1. R. S. Gaonkar, Microprocessor Architecture, Programming, and Applications with the 8085, Fifth Edition, Penram International Publishing (India) Private Limited.
  2. S Ghoshal, Microprocessor Based System Design, Macmillan India Limited, 1996
  3. M. Mano, Digital Logic and Computer Design, Prentice – Hall India
  4. B. Ram - Fundamentals of Microprocessor and Microcontrollers
  5. “Microprocessors: Principles and Applications” by A Pal
  6. “Microprocessors and Microcontrollers : Architecture, Programming and Interfacing Using 8085, 8086 and 8051” by Soumitra Kumar Mandal
  7. “Introduction to Microprocessors and Microcontrollers” by Crisp John Crisp
  8. “Microprocessors And Microcontrollers” by A Nagoor Kani
  9. “Microprocessors And Microcontrollers : Architecture, Programming and System Design 8085, 8086, 8051, 8096” by Krishna Kant
  10. “8 - Bit Microprocessor” by Vibhute

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