(SEM VI) THEORY EXAMINATION 2024-25 MICROPROCESSOR

BEE602 – MICROPROCESSOR

Section-Wise Solved Answers (2024–25)

SECTION A

Attempt all questions in brief (2 × 7 = 14 marks)

(a) Which interrupt has the highest priority in 8085?

Among the interrupts INTR, TRAP, RST 6.5 and RST 7.5, TRAP has the highest priority. TRAP is a non-maskable interrupt and is edge as well as level triggered. It is mainly used for emergency situations such as power failure.

(b) In 8085 name the 16-bit register.

In the 8085 microprocessor, both the Stack Pointer (SP) and the Program Counter (PC) are 16-bit registers. Hence, the correct answer is both (i) and (ii).

(c) Access time is faster for which memory?

Among ROM, SRAM, DRAM and EPROM, SRAM has the fastest access time because it does not require refresh cycles and has a simpler internal structure.

(d) What do you understand by Min/Max mode of 8086 microprocessor?

The 8086 microprocessor can operate in two modes: Minimum mode and Maximum mode.
Minimum mode is used for single-processor systems where the 8086 itself generates all control signals. Maximum mode is used in multi-processor systems where control signals are generated by an external controller such as the 8288.

(e) How large is the instruction queue of the 8086?

The 8086 microprocessor has a 6-byte instruction queue. This queue supports pipelining and improves execution speed by fetching instructions in advance.

(f) Write basic differences between 8085 and 8086 microprocessor.

The 8085 is an 8-bit microprocessor with a 16-bit address bus, while the 8086 is a 16-bit microprocessor with a 20-bit address bus. The 8086 supports pipelining and has more registers, higher speed, and larger memory addressing capability than the 8085.

(g) Define the LDA instruction of 8085.

The LDA (Load Accumulator Direct) instruction loads the contents of a specified memory location directly into the accumulator. It uses direct addressing mode and requires three bytes.

SECTION B

Attempt any three (7 × 3 = 21 marks)

(a) Define T-state and in which T-cycle the ALE signal is activated?

A T-state is the smallest unit of time in a microprocessor and corresponds to one clock period.
The ALE (Address Latch Enable) signal is activated during the first T-state (T₁) of the machine cycle to latch the lower-order address from the multiplexed address/data bus.

(b) Explain the block diagram of 8085 microprocessor.

The block diagram of the 8085 consists of the Arithmetic and Logic Unit (ALU), register array, instruction decoder, timing and control unit, interrupt control, serial I/O control, and address/data buffers.
The ALU performs arithmetic and logical operations. Registers temporarily store data. The timing and control unit generates control signals, while the interrupt control unit manages interrupts.

(c) Explain the seven-segment display with suitable diagram.

A seven-segment display consists of seven LEDs arranged in the form of the number 8. By energizing different combinations of segments, digits from 0 to 9 can be displayed.
It can be either common anode or common cathode type. Seven-segment displays are widely used in digital clocks, calculators, and display units interfaced with microprocessors.

(d) Define branching operation of 8085 with an example.

Branching operations change the normal sequence of program execution. These instructions allow the program to jump to a specified memory location based on a condition.
For example, JNZ LOOP transfers control to the label LOOP if the zero flag is not set.

(e) Explain RS-232C pin diagram and functioning.

RS-232C is a standard for serial communication. It uses signals such as TXD, RXD, RTS, CTS, DTR, and DSR for data transfer and control.
It enables communication between a computer and peripheral devices like modems and microprocessor-based systems using serial data transmission.

(f) Explain how many times the following loop will be executed in 8085.

LXI B, 0007H LOOP: DCX B JNZ LOOP 

The register pair BC is initialized with 0007H. The instruction DCX B decrements BC by 1 each time. The loop continues until BC becomes 0000H.
Therefore, the loop will execute 7 times.

SECTION C

Q3. Attempt any one

(a) What are the various registers in 8085 and their sizes?

The 8085 microprocessor has several registers. The accumulator is an 8-bit register used for arithmetic and logic operations. General-purpose registers B, C, D, E, H, and L are also 8-bit. The Program Counter and Stack Pointer are 16-bit registers. Flag register is 8-bit and stores status flags.

(b) Explain the pin diagram of 8086 microprocessor.

The 8086 has 40 pins classified into address/data pins, control pins, interrupt pins, and power pins. Address and data lines are multiplexed. Control pins manage memory and I/O operations. Interrupt pins handle external interrupts, enabling efficient system operation.