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Intel 8086 and 8088

The Intel 8086/8088 family of microprocessors is a 16 bit architecture on a 16 bit (8086) or an 8 bit (8088) bus. The 8088 was the processor in the original IBM PC, and has evolved into the most popular processor used today in PC's and servers.

1,056 Questions

How does the microprocessor work?

Suppose we give a 8-bit instruction ADD B to the microprocessor

then this instruction is not at all understood by microprocessor as it only accepts binary inputs

so first of all it stores the instruction in the INSTRUCTION REGISTOR

then it decodes this instruction ADD B to its suitable binary code 80H in the INSTRUCTION DECODER.. after converting to 80H then the microprocessor understands that ..

yes i have to add the content of the resistor B with that of A(accumulator) and store the result in the accumulator A

this is a small example how microprocessor operates facing the instructions

What is the difference between a permanent address and a care of address?

A permanent address for a mobile node is it's IP address when it is at it's home network. A care-of-address is the one its gets when it is visiting a foreign network.

What is the average speed for a central processing unit?

The answer is at best a moving target; the average six months from now will almost certainly be different. Also, "average" how, and over what population? All laptops still in use? All laptops currently being sold? All laptops currently being manufactured? Do underpowered "netbooks" count? The question is so vague as to be effectively meaningless.

Why all the 16 address lines are not act as a data lines in 8085 microprocessor?

the 8085 microprocessor is a 8-bit microprocessor and these are bidirectional but the address lines are unidirectional.these address lines are used to address the location of the instruction in memory .these data lines are used to transfer data between processor and peripheral devices. when the address of the instruction will be recognized by the address lines the data will be send to the processor

therefore the 16 address lines are not act as a data lines in 8085

How physical address is generated in 8086 microprocessor?

For the formation of physical address we need Segment address and offset address

Consider an example

Segment Address : 1005H

Offset Address : 5555H

Segment address : 1005H 0001 0000 0000 0101

Shifted by 4 bit positions : 0001 0000 0000 0101 0000

Offset Address : + 0101 0101 0101 0101

Physical Address : 0001 0101 0101 1010 0101

1 5 5 A 5 H

Physical Address of given Segment Address : 155A5H

What is TEST pin in 8086 in microprocessor?

TEST This input is examined by a 'WAIT' instruction. If the TEST input goes low,

execution will continue, else, the processor remains in an idle state. The input is

synchronized internally during each clock cycle on leading edge of clock.

What is the size of flag register?

All of the 8086/8088 registers, AX, BX, CX, DX, SP, BP, SI, DI, CS, DS, SS, ES, IP, and FLAGS, are 16 bit registers. The AX, BX, CX, and DX registers may also be viewed as 8 eight bit registers AH/AL, BH/BL, CH/CL, and DH/DL.

What is a bus specify the function of address bus and direction of information flow on the address bus?

A bus is a collection of conducting wires which connect the processor and other devices in parallel scheme.

The function of an address bus is to carry the address of the memory locations from the processor to the memory device, the address bus is unidirectional(only in one direction) in this processor so the flow of information on this bus is from the microprocessor to the attached device(memory module).

What is ALE in 8086 in microprocessor?

ALE is a signal that means that the data bus contains the lower order address bus values. External hardware should strobe the data bus during ALE time, and lock it on the falling edge of ALE.

Why was segmentation originally introduced in 8088 architecture?

Memory segmentation is an attempt to address more memory than the processor architecture would normally allow.

In the case of the 8086/8088, a 16 bit processor, you would normally expect addressibility of 64 kb, because that is what the instruction set is capable of developing as an effective address, either in the case of a direct address, an indirect address, or an indexed address, since all of its registers are 16 bits in size.

What Intel did was provide four more registers called segment registers which would provide the base address of an address in physical memory to which the processor generated effective address would be added. The segment register is still 16 bits in size, but it is left shifted by four before being added to the effective address. This creates a physical address that is 20 bits in size, for a total address range of 1 mb.

Note that you are still constrained to a segment size of 64 kb, in that you must stay within 64 kb unless you intend to change the value of one of the segment registers. This hampers the ability to access any arbitrary location in memory, effectively making it a two step operation - load the segment register - then access the offset address.

In the 8086/8088 there are four segment registers; Code Segment (CS), Data Segment (DS), Stack Segment (SS), and Extra Segment (ES). All opcode access is from CS. Default data access is from DS, unless a segment prefix is applied. All stack operations are from SS. Certain repeated string operations take place between DS and ES.

Because of the segmented architecture, the concept of near and far grew up with the original PC and DOS and Windows. Basically, a near address was a 16 bit address that assumed the current segment, while a far address was a 32 bit address that contained both a segment and an offset. Note that the concept of a flat 32 bit address did not come into full play until true 32 bit operating systems hit the street, and that did not occur until the introduction of the 80386.

What is the max ram for a 20 wire CPU address bus?

220 or 1,048,576 locations, otherwise known as 1 meg. If its an 8 bit bus, we are talking about 1 megabyte. That happens to be the size of the address bus of the original 8086/8088 microprocessor.

What are the kinds of microprocessors?

A microprocessor is a chip that serves as the central processing unit (CPU) in personal computer(PCs). it is often called a logic chip or master chip. it controls all programs and performs arithmetic calculations with great accuracy. it acts as the 'brain' of the computer.

example:-

Intel 4004 , Intel 8080 , Intel Pentium Pro , Pentium Microprocessor.

How much virtual memory can be address with 16 bit address bus?

You can address 2^20 (or 1,048,576) locations. Each location will consist of 16 bits (1 or 0) which is commonly called a Word (though that isn't always the case).

I think what you're really looking for is the answer in bytes. Each data bus line holds a bit, 8 bits is a byte, so you're data line is 2 bytes. Since each location holds two bytes, this would be 2,097,152 bytes, or 2MB

What is the purpose of DI register in microprocessor in 8086?

DI is the Index register in Data segment(16-bit, 64 KB) .

Destination Index (DI) is a 16-bit register. DI is used for indexed, based indexed and register indirect addressing, as well as a destination data address in string manipulation instructions.

What is the purpose of a PC?

To provide personal computing power to individual users.

What is the difference between 8080 and 8086?

The major difference between the 8085 and the 8086/8088 is that the 8085 is an 8 bit computer, and the 8086/8088 is a 16 bit computer.

How many data lines in 8086?

There are eight datalines, D0 through D7, in the 8085 microprocessor. They are shared, or multiplexed with the eight low order address lines, A0 through A7, and are called AD0 through AD7 on the pinout drawing.

How many flag registers are there in 8085?

We have only one flag register of 8 bits.

Bits description is as follows (Assuming D0=LSB & D7=MSB)

D7=Sign Bit.

D6= Zero Flag

D4= Auxiliary Carry Flag

D2 = Parity Flag

D0= Carry Flag.

Why 8085 is called 8-bit processor and why 8086 is called 16-bit?

The 8086/8088 processor is called a 16 bit processor because its basic architecture is 16 bits wide. Its registers and accumulator are 16 bits wide, and the primary data it manipulates without extra work is 16 bits wide.

Why interrupt handlers are written in assembly language?

When an interrupt is requested, the currently running process is suspended and the handler is

invoked. When the handler exits, control is handed back to the running process. Since interrupts are

practically random and unplanned, when the handler passes back control, it must ensure that all

registers and stacks that it used are restored back to the exact state they were in when the process

got interrupted, so that the process can resume like as though nothing happened.

Access to these registers and stacks can only be done in assembly.

Other reasons include the fact that interrupt handlers must be very fast, and since the interrupt

routines are very short, they can be hand‐crafted to be much faster than anything a compiler

generates.

Do 8086 have in built clock?

The 8086/8088 has a clock oscillator circuit. You provide a crystal, and it will generate a clock signal that controls the speed of the processor. In that respect, it has a clock.

The 8086/8088, however, does not have a time of day or date clock. You can build a software entity that keeps day/date time using interrupts from a divider off of the clock oscillator but, that is not the same thing as a non-volatile clock chip such as provided in the PC, but which is not part of the 8086/8088.