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