It is the collection of last four semester two mark question with answer. It is very useful for EEE students

1. MICROPROCESSORS AND MICROCONTROLLER
Two Marks - University Question Bank (April / May – 2015)
1. What is the function of ALE in 8085 microprocessor?
ALE is a control signal of 8085 MPU. 8085 is a 8-bit microprocessor which have
16-bit address bus among them lower 8-bit are multiplexed. So while MPU executes read
or write operation it needs to de multiplexed. ALE control signal used to de multiplexed
the lower order address and data bus.
2. What is the maximum number of byte of memory addressable by the 8086
microprocessor?
1 Mb since the 8088/ 8086 has 20 bit address lines so 220 = 1Mb
3. What is the function of Rotate Instructions? Give an example.
Rotate instructions are similar to shift instructions, except that rotate instructions
are circular, with the bits shifted out one end returning on the other end. Rotates can be
to the left or right. Rotates can also employ an extend bit for multi-precision rotates.
Example: RRC, RLC
4. How is time delay generated using subroutines.
Subroutine is one that generates a programmable Time delay. Time delays may
be done by using software loops that essentially do nothing for some period.
5. What are the internal Registers available in 8259 PIC?
 In service Register
 Priority Resolver
 Interrupt Mask Register
 Interrupt Request Register
6. Distinguish between synchronous and asynchronous transmission.
Synchronous transmission:
 Supports high data transfer rate
 Needs clock signal between the sender and the receiver
 Requires master/slave configuration
Asynchronous transmission:
 Does not need clock signal between the sender and the receiver
 Slower data transfer rate
7. Write down the instruction format for 8051 microcontroller.
 One Byte Instruction
 Two Byte Instruction
 Three Byte Instruction
8. What is the purpose of timing diagram in 8051 microcontroller?
The graphical representation of all steps which are performed in a machine cycle
is known as the timing diagram. Timing diagram consist of op code fetch, memory read,
memory write, I/O read and I/O write operations.
9. How pulse is generated using 8051 microcontroller.
 Sequential Approach
 Time multiplexed Approach
10. What are the control signals from 8051 microcontroller required for
washing machine control?
Inputs:
 Start
 Prewash Input
 Cloth Type
Outputs:
 Prewash Output
 Main Wash1
 Main Wash 2
 Rinse1
 Rinse 2
 Graduated Spin

2. Two Marks - University Question Bank (Nov / Dec – 2014)
1. State the function of the Keyboard Interrupts.
In computing, a keyboard controller is a device that interfaces a keyboard to a
Microprocessor. Its main function is to inform the Microprocessor when a key is pressed
or released. When data from the keyboard arrives, the controller raises an interrupt (a
keyboard interrupt) to allow the CPU to handle the input.
2. List the 8085 Flags.
 Sign
 Zero
 Auxiliary Carry
 Parity
 Carry
3. List any two data Manipulation Instructions.
 Data Transfer
 Arithmetic
 Logical
4. What is meant by Look up Table?
A lookup table is an array that replaces runtime computation with a simpler
array indexing operation. The savings in terms of processing time can be significant,
since retrieving a value from memory is often faster than undergoing an 'expensive'
computation or input/output operation.
5. What are the functions of USART?
USART stands for universal Synchronous / Asynchronous Receiver / Transmitter.
It is a programmable communication interface that can communicate by using either
synchronous or asynchronous serial data.
6. List out the Operating Modes in 8253 Timer / Counter.
Each of the three counters of 8253 can be operated in one of the following six
modes of operation.
1. Mode 0 (Interrupt on terminal count) 2. Mode 1 (Programmable mono shot)
3. Mode 2 (Rate generator) 4. Mode 3 (Square wave generator)
5. Mode 4 (Software triggered strobe) 6. Mode 5 (Hardware triggered strobe)
7. Mention the registers used Serial Communication in 8051 Microcontroller.
 SCON – Serial Control Register
 SBUF – Serial Data Buffer
8. What are the addressing Modes followed in 8051 Microcontroller?
 Direct addressing
 Register addressing
 Register indirect addressing
 Implicit addressing
 Immediate addressing
 Index addressing
 Bit addressing
9. What are the I/O instructions used in 8051?
10. State the principle of Microcontroller based Stepper motor control system.
A Stepper motor is a Digital Motor. It can be driven by digital signal. Consider a
Four winding motor. These windings are connected to the 12V supply. Due to this, motor
can be excited by grounding four terminals of the four windings. Motor can be rotated in
steps by giving proper excitation sequence to these windings. The lower Nibble of Port 1
of the 8051 is used to generate excitation signals in the proper sequenc e.

3. Two Marks - University Question Bank (April / May – 2014)
1. To obtain a 320 ns clock, What should be the input clock Frequency? What is
the Frequency of clock signal at CLK OUT?
2. What is meant by Level Triggered Interrupt? Which of the Interrupts in 8085
are level Triggered?
A level-triggered interrupt is an interrupt signalled by maintaining the interrupt
line at a high or low level. A device wishing to signal a Level-triggered interrupt drives
the interrupt request line to its active level (high or low), and then holds it at that level
until it is serviced. It ceases asserting the line when the CPU commands it to or
otherwise handles the condition that caused it to signal the interrupt.
3. Mention the Similarities and difference between Compare and Subtract
Instructions.
The compare and subtract instructions in the 8085 both subtract one operand
from another, and set flags accordingly. The subtract instruction stores the result in the
accumulator, while the compare instruction does not - except for the flags, the compare
instruction "throws" the result away.
4. State the Purpose and Importance of NOP Instruction.
No operation is performed. The instruction is fetched and decoded. However no
operation is executed.
5. What are the salient features of INTEL 8259 Programmable Interrupt
Controller?
6. How data is transmitted in Asynchronous serial communication.

4. 7. Mention the Purpose of PSEN and EA in 8051 Microcontroller.
8. List the Interrupts sources in 8051 Microcontroller.
9. State the functions performed by JBC and CJNE instruction sin 8051
Microcontroller.
JBC:
CJNE:
10. What is Program Status word?

5. Two Marks - University Question Bank (April / May – 2013)
1. What is the function of Program Counter in 8085 Microprocessor?
It is a 16 bit special function register in the 8085 microprocessor. It keeps track
of the next memory address of the instruction that is to be executed once the execution
of the current instruction is completed. In other words, it holds the address of the
memory location of the next instruction when the current instruction is executed by the
microprocessor.
2. How many address and Data lines are used in 8086 Microprocessor?
 Address Line – 16 Bits
 Data Line – 16 Bits
3. What is the different Machine control instructions used in 8085
Microprocessor?
EI - Enable Interrupt System
DI - Disable Interrupt System
HLT - Halt
NOP - No Operation
SIM – Set Interrupt Mask
RIM – Reset Interrupt Mask
4. What is the function of Stack?
A stack pointer is a small register that stores the address of the last program
request in a stack. A stack is a specialized buffer which stores data from the top down.
As new requests come in, they "push down" the older ones. The most recently entered
request always resides at the top of the stack, and the program always takes requests
from the top.
A stack (also called a pushdown stack) operates in a last-in/first-out sense. When
a new data item is entered or "pushed" onto the top of a stack, the stack pointer
increments to the next physical memory address, and the new item is copied to that
address. When a data item is "pulled" or "popped" from the top of a stack, the item is
copied from the address of the stack pointer, and the stack pointer decrements to the
next available item at the top of the stack.
5. What are the different peripheral interfacing used with 8085 Microprocessor.
Peripheral Interfacing is considered to be a main part of Microprocessor, as it is
the only way to interact with the external world. The interfacing happens with the ports
of the Microprocessor.
The main IC's which are to be interfaced with 8085 are:
1. 8255 PPI
2. 8259 PIC
3. 8251 USART
4. 8279 Key board display controller
5. 8253 Timer/ Counter
6. A/D and D/A converter interfacing.
6. What is the Output Terminal in USART 8251?
TXD – Transmitter
TXRDY – Transmitter Ready
TXE – Transmitter Enable
RXRDY – Receiver Ready
DTR – Data Terminal Ready
RTS - Request to Send
7. What are the Addressing Modes of 8051 Microcontroller?
 Register Addressing
 Direct Byte Addressing
 Register Indirect Addressing
 Immediate Addressing
 Register Specific Addressing
 Index Addressing

6. 8. What is the function of R register in 8051 Microcontroller?
This is a common name for 8 general-purpose registers (R0, R1, R2 ...R7). Even
though they are not true SFR’s, they deserve to be discussed here because of their
purpose. They occupy 4 banks within RAM. Similar to the accumulator, they are used for
temporary storing variables and intermediate results during operation. Which one of
these banks is to be active depends on two bits of the PSW Register. Active bank is a
bank the registers of which are currently used.
9. Write an Assembly language program to receive input from port P1.5 and if it
is high then an output 35H is sent to Port 0. What are I/O instructions in 8051
Microcontroller?
SETB P1.5 ; make P1.5 an input
MOV A, #35H
AGAIN: JNB P1.5, AGAIN ; get out when P1.5 = 0
MOV P0, A ; issue A to P0
END
 Bit Level Instruction is used for I/O Instruction in 8051
10. How is pulse generated from Microcontroller for stepper motor control?
The stepper motor winding is connected to microcontroller through driver circuit
or Darlington pair arrangement and another end of the winding is connected to the
ground Potential. The out put of microcontroller is very minimum (mA), it is not enough
for the drive the motor winding so separate driver circuit is needed. The pulses are
generated through PWM technique.