UNIT I: Introduction to Basic Microprocessors Questions and Notes

UNIT I: Introduction to Basic Microprocessors: Historical Background, the Harvard and Princeton architecture, The Microprocessor-Based Personal Computer Systems. The Microprocessor 8085, 8088 basics and comparison (Block & Pin diagram only).

syllabus source:

https://csvtu.ac.in/ew/download/b-tech-5th-semester-5/?wpdmdl=14364&refresh=63c10f5a398271673596762

Prerequisite: Study the following Block diagram first to answer the Questions.

1. Block diagram for the Harvard and Princeton architecture.

2. Block Diagram for Microprocessor 8085

3. Pin Diagram for Microprocessor 8085

4. 8085 vs 8088

Questions: Compiled from previous year CSVTU QPs

1. Write the Difference between Harvard & Princeton Architecture.

👉Note: The Von Neumann (a.k.a. Princeton) architecture.

Difference Between Von Neumann and Harvard Architecture

Parameters	Von Neumann Architecture	Harvard Architecture
Definition	The Von Neumann Architecture is an ancient type of computer architecture that follows the concept of a stored-program computer.	Harvard Architecture is a modern type of computer architecture that follows the concept of the relay-based model by Harvard Mark I.
Physical Address	It uses one single physical address for accessing and storing both data and instructions.	It uses two separate physical addresses for storing and accessing both instructions and data.
Buses (Signal Paths)	One common signal path (bus) helps in the transfer of both instruction and data.	It uses separate buses for the transfer of both data and instructions.
Number of Cycles	It requires two clock cycles for executing a single instruction.	It executes any instruction using only one single cycle.
Cost	It is comparatively cheaper in cost than Harvard Architecture.	It is comparatively more expensive than the Von Neumann Architecture.
Access to CPU	The CPU is not able to read/write data and access instructions at the same time.	The CPU can easily read/write data as well as access the instructions at any given time.
Uses	This method comes to play in the case of small computers and personal computers.	This architecture is best for signal processing as well as microcontrollers.
Requirement of Hardware	As compared to Harvard Architecture, Von Neumann Architecture requires lesser architecture. It is because it only needs to reach one common memory.	This one requires more hardware. It is because it requires separate sets of data as well as address buses for individual memory.
Requirement of Space	This architecture basically requires less space.	This architecture comparatively requires more space.
Usage of Space	This architecture does not waste any space. It is because the instruction memory can utilize the left space of the data memory. It can also happen vice-versa.	This type of architecture can result in space wastage. It is because the instruction memory cannot utilize the leftover space in the data memory. It also cannot happen vice-versa.
Execution Speed	The speed of execution of the Von Neumann Architecture is comparatively slower. It is because it is not capable of fetching the instructions and data both at the same time.	The overall speed of execution of Harvard Architecture is comparatively faster. It is because the processor, in this case, is capable of fetching both instructions and data at the very same time.
Controlling	The process of controlling becomes comparatively simpler with this architecture. It is because it fetches either instructions or data at any given time.	The process of controlling becomes comparatively complex with this architecture. It is because it basically fetches both instructions and data simultaneously at the very same time.

2. Draw & Explain the Internal Architecture of 8085 in brief.

or
Explain the internal architecture of 8085 microprocessor with basic functional block.

Ans: 

3. Give Classification of Pin in 8085 with neat Diagram

Ans: Pin Diagram of 8085:

The pins of a 8085 microprocessor can be classified into seven groups:

Address bus: A15-A8

Data bus: AD7-AD0, it carries the least significant 8-bit address and data bus.

Control and status signals: Control signals are RD, WR & ALE, Status signals are IO/M, S0 & S1

Power supply: VCC & VSS.

Clock signals: 3 clock signals, i.e. X1, X2, CLK OUT

Interrupts & externally initiated signals: There are 5 interrupt signals, i.e. TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR.

HOLD , HLDA (HOLD Acknowledge).

Serial I/O signals: SID and SOD. 

Classification of Signals:

4. Give Comparison between Microprocessor 8085 and 8086.

Ans. Also refer the Architecture and pin diagram of 8085 and 8086.

Comparison between 8085 & 8086 Microprocessor 

  Size − 8085 is 8-bit microprocessor, whereas 8086 is 16-bit microprocessor. 

 Address Bus − 8085 has 16-bit address bus while 8086 has 20-bit address bus. 

 Memory − 8085 can access up to 64Kb, whereas 8086 can access up to 1 Mb of memory. 

 Instruction − 8085 doesn’t have an instruction queue, whereas 8086 has an instruction queue. 

 Pipelining − 8085 doesn’t support a pipelined architecture while 8086 supports a pipelined architecture. 

 I/O − 8085 can address 2^8 = 256 I/O's, whereas 8086 can access 2^16 = 65,536 I/O's. 

 Cost − The cost of 8085 is low whereas that of 8086 is high.

5. Give Pin Diagram of 8086 with neat label of pin Diagram.

o   8086 Microprocessor is an enhanced version of 8085 Microprocessor 

    Designed by Intel in 1976.It is a 16-bit Microprocessor, 20 address lines 16 data lines, Provides up to 1MB storage. It consists of powerful instruction set, which provides operations like multiplication and division easily.

6. Draw the Internal Architecture of 8086 and Explain the function of each unit of the same in brief.

Ans: 

The internal architecture of Intel 8086 is divided into 2 units: 

The Bus Interface Unit (BIU), and The Execution Unit (EU). 

8086 Architecture

Memory segmentation: 

• In order to increase execution speed and fetching speed, 8086 segments the memory. 
• Its 20-bit address bus can address 1MB of memory, it segments it into 16 64kB segments. 
• 8086 works only with four 64KB segments within the whole 1MB memory.

7. Explain the functions of the following signals of 8085.

(1)  ALE

(ii)  IO/M

(iii) RD

(iv) READY

(v) TRAP

(vi) INTR & INTA

(vii) HOLD & HLDA

(viii) RESET IN

Ans: Refer pins of 8085

Q. 8085 vs 8086 vs 8088

The architecture of 8088 is same as 8086 architecture, but there are two changes. The 8088 has a 4-byte instruction queue in place of 6-byte instruction queue in 8086 and the data bus of 8088 is 8-bit.

There is no concept of even-address bank and odd-address bank of memory in 8088.

As the data bus is 8-bit, the 8088 can access only a byte at a time. Therefore, the speed of operation of 8088 will be reduced as compared to 8086, though internal data bus of 8088 is 16 bits and it can process the 16-bit data internally. 

DIFFERENCES:

8085	8086	8088
8085 is an 8 bit microprocessor.	8086 is a 16 bit microprocessor.	8088 is a 16 bit microprocessor.
It has 8 bit data bus.	😃It has 16 bit data bus.	😃It has 8 bit data bus.
It has 8 bit ALU.	It has 16 bit ALU.	It has 16 bit ALU.
8085 does not require memory banking as it has an 8 bit data bus.	8086 requires memory banking to transfer 16 bit data at a time.	8088 does not require memory banking as it has an 8 bit data bus.
8085 performs slower memory operations as it can transfer only 8 bits in one cycle.	8086 performs faster memory operations as it can transfer 16 bits in one cycle.	8088 performs slower memory operations as it can transfer only 8 bits in one cycle.
8085 does not support pipeline architecture.	8086 supports pipeline architecture.	8088 supports pipeline architecture.
8085 has no pre-fetch queue as it does not support pipelining.	8086 has a 6 byte pre-fetch queue for pipelining.	😃8088 has a 4 byte pre-fetch queue for pipelining.
8085 has an IO/ pin to differentiate between memory and I/O operations.	8086 has an M/ pin to differentiate between memory and I/O operations.	8088 has an IO/ pin to differentiate between memory and I/O operations.
8085 has no pre-fetchqueue.	8086 BIU will fetch new bytes into the pipelining queue when 2 bytes of the queue are empty.	8088 BIU will fetch a new byte into the pipelining queue when 1 byte of the queue is empty.
8085 has 5 flags.	8086 has 9 flags.	8088 has 9 flags.

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