Question

[CS] = A000DH and [IP] = 1234H in 8086 system. What would be the 20-bit
physical address which would be generated?

Answer 1

Answer:

The offset of the CS Register is the IP register.

Therefore, the effective address of the memory location pointed by the CS register is calculated as follows:

Effective address= Base address of CS register X 10H + Address of IP

Explanation:

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Answer 2

Answer:

The IP register is the offset of the CS Register.

As a result, the following formula is used to calculate the effective address of the memory location referenced by the CS register:

Base address of CS register X 10H + IP address = Effective address

Explanation:

Memory Segmentation is a notion of the 8086. It is a process in which the entire memory is partitioned (segmented) into smaller portions known as segments. Code Segment (CS), Stack Segment (SS), Data Segment (DS), and Extra Segment (ES) are the different types of segments (ES)

Each Segment has a 16-bit Segment Register that contains the Segment's Base Address (beginning Address). Out of 1MB of memory, the 8086 can address 16-bit x 64KB = 256 KB at any given time.

The address line on the 8086 is 20 bits. As a result, the maximum address that an 8086 can address is $2^{20}$ = 1MB. As a result, the 8086 can address addresses spanning from 00000 H to FFFFF H. This 1MB RAM is broken down into 16 logical segments, each having 64KB of memory.

The physical address of a memory location is required to locate any address in the memory bank. The 8086 Address Line and 16-bit Segment Registers alone are insufficient to obtain the 20-bit Physical Address.

You can't directly address a memory location with a 20-bit address to the processor. You must specify the 16-bit address in terms of the segment. The offset refers to the 16-bit address in relation to the section (64KB segment) of the memory bank.

So, Physical Address = Base Address + Offset.

Assume the Data Segment's Base Address is 1000h, and the data you require is stored in the Data Segment's 0020h memory location (Offset). The following is how the real address is calculated.

1. Left shift the segment register's 16-bit address by 4-bits 0001 0000 0000 0000. (0000)

2. To this shifted base address, add the 16-bit offset address.

So, the actual address turns out to be 10020h.

Therefore, at any point of time we can change the base address of the segment registers and use the memory locations in those segments using the offset.

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