A microprocessor is a semiconductor chip fabricated with entire central processing unit (CPU) on it. It is a programmable device that accepts binary data from an input device, processes the data according to the instructions stored in the memory and provides results as output. Basically microprocessor performs two functions - (a) Fetches an instruction from the memory and (b) Performs the operation specified by the instruction. There are special inputs to the microprocessor called interrupts. External devices use these interrupts to get the microprocessor attention. A micro computer can be built by using 8085 microprocessor along with many other chips such as 8155, 8255, 8279, 8253, 8257, 8259, 8251 etc. 8085 microprocessor is 8-bit microprocessor which has 8-bit data registers where as 8086 is a 16-bit microprocessor.
The technique of assigning a memory address to each I/O device in the computer system is called :
Memory - Mapped I/O
The name says exactly what the technique does. In memory-mapped I/O each peripheral register is given an address out of the processor's ordinary memory space, so the CPU talks to it with the same instructions it uses for memory — option 4.
The alternative is I/O-mapped I/O, also called isolated or peripheral-mapped I/O, in which peripherals live in a separate address space of their own, reached only by the dedicated IN and OUT instructions. Option 1 names precisely that opposite scheme, which is why it is the attractive wrong answer here.
| Memory-mapped I/O | I/O-mapped (isolated) I/O | |
|---|---|---|
| Address space | Shares the 64 KB memory map | Separate 256-port space |
| Address lines used | All 16 | Lower 8, duplicated on A8–A15 |
| Instructions | Any memory instruction — MOV, LDA, ADD M, ANA M | Only IN and OUT |
| Control signal | IO/M = 0 | IO/M = 1 |
| Cost | Consumes memory addresses | Memory space untouched |
| Speed | Slower — 16-bit address to decode | Faster — 8-bit address |
The 8085 supports both, and the IO/M pin is what distinguishes them: the address decoder is simply wired to include or ignore that line. If the decoder ignores IO/M entirely, the device answers to a memory address and the scheme is memory-mapped.
Why anyone would spend memory addresses on peripherals. The gain is the full instruction set. A memory-mapped port can be tested with ANA M, incremented with INR M or added to the accumulator directly, whereas an isolated port must first be brought in with IN before anything can be done to it. That flexibility is why almost every modern processor — ARM and RISC-V among them — is purely memory-mapped and has no separate I/O space at all; the x86 family, with its IN/OUT instructions, is the notable survivor of the other tradition.
Options 2 and 3, "ported I/O" and "dedicated I/O", are not standard terms for either scheme.
Hence, the technique is called memory-mapped I/O.
Similar Questions
A microprocessor is a semiconductor chip fabricated with entire central processing unit (CPU) on it. It is a programmable device that accepts binary data from an input device, processes the data according to the instructions stored in the memory and provides results as output. Basically microprocessor performs two functions - (a) Fetches an instruction from the memory and (b) Performs the operation specified by the instruction. There are special inputs to the microprocessor called interrupts. External devices use these interrupts to get the microprocessor attention. A micro computer can be built by using 8085 microprocessor along with many other chips such as 8155, 8255, 8279, 8253, 8257, 8259, 8251 etc. 8085 microprocessor is 8-bit microprocessor which has 8-bit data registers where as 8086 is a 16-bit microprocessor.
The following 8051 assembly program is given. Answer the questions based on it.
Line No. Mnemonics 1 MOV SP, #4F H 2 SET B PSW.3 3 MOV R0, #25H 4 MOV R1, #0AH 5 MOV R2, #06H 6 PUSH 8 7 PUSH 9 8 PUSH 0AH . . . V V 20 POP 8 $D_7$ $D_6$ $D_5$ $D_4$ $D_3$ $D_2$ $D_1$ $D_0$ In 8255 programmable peripheral interface device, if the port A and port B are to be set in a hand shake mode along with port C, what are the bits in the 8 bit control word to be set as 0 1 0.
The number system for the machine code of the microprocessor 8085 is
Which of the options in a multipurpose instruction used to implement the interrupt of 8085 and serial data input ?
Both 8155 and 8255 programmable peripheral interface ICs have the following common features :
(i) Programmable I/Os
(ii) Either port A or Port B can be set as either input or output ports.
(iii) One 14-bit down counter
(iv) AD0 – AD7 are multiplexed address/datalines.Each instruction in an assembly program has the following fields :
(i) Lable field
(ii) Operand field
(iii) Comment field
(iv) Mnemonic fieldPlease write the proper sequence of fields :
The mnemonic of 8085 processor indicate :
List – I List – II a. RLC i. Rotate Accumulator Right through carry b. RRC ii. Rotate Accumulator Left through carry c. RAR iii. Rotate Accumulator Left d. RAL iv. Rotate Accumulator Right Codes :
Match the following :
List – I (Pin terminals) List – II (Applications) a. SID, SOD i. Wait state b. READY ii. Serial data transfer c. TRAP iii. Address Latch Control d. ALE iv. Interrupt Codes :
Assertion (A) : In serial communication system, when the transmission of data goes in both ways, it is called full-duplex system. Now if two micro processors are connected in full duplex mode, the amount of data transmitted will be double to the amount of data in half-duplex mode connection.
Reason (R) : When the transmission of data goes in one way, it is called half-duplex system and when the data moves in both ways, it is called full duplex system.
Important Questions from Microprocessors
An 8086 address bus is a/an _____ -bit bus
Program counter for any counter:
In the pin out configuration of the 8085 microprocessor, the sequential input data is represented by
Which of the following functions is not performed by a microprocessor?
Match the columns.
Pin
Description
a. D 0-D 7
1. Reset Input
b. RESET
2. Data Lines
c. A 0,A 1
3. Internal Address
