Control Memory

• The function of the control unit in a digital computer is to initiate sequences of

microoperations.

• Hardwired control is when control signals are generated by actual hardware circuitry.

• Microprogrammed control is performed by software using a technique called

microprogramming.

• Microprogramming is simply a series of sequential microoperations specifed by control

words.

• A control word is simply a sequence of 0's and 1's that specify microinstruction.

• And, a sequence of microinstructions constitues a microprogram.

• A computer that employs a microprogrammed control has two separate memories: a main
memory and a control memory.

• User programs are loaded into main memory. However, control memory holds a fixed
microprogram, stored in ROM, that cannot be altered.

• What fundamental advantage does microprogrammed control have over hardwired

control?

• What about disadvantages?

• Executing control microinstructions is similar to executing regular instructions.

o Address of microinstruction is placed in the control memory address register.

o The microinstruction is fetched from control memory and placed in the control
data register.
o The microperations specified by the microinstruction are performed.
o The address of the next microinstruction is determined and the process repeats
itself.

• The address sequencer is used to determine the address of the next microinstruction.

• The sequencer utilizes a pipeline register to hold the next address. Hence, while the
current microinstruction is being executed, the next instruction is being loaded into the
pipeline register.
1. A Compiler is ____

a program which a program which

a combination of translates from one translates from one
None of these
computer hardware high-level language to high-level to a
another machine level
•

2. When a key is pressed on the keyboard, which standard is used for converting the
keystroke into the corresponding bits

ANSI ASCII EBCDIC ISO

•

3. A Pixel is

A computer The smallest

A picture stored in
program that draws resolvable part of a None of these
secondary memory
picture picture
•

4. Which device is used as the standard pointing device in a Graphical User Environment

Keyboard Mouse Joystick Track ball

•

5. Which number system is usually followed in a typical 32-bit computer?

2 10 16 32
•

6. Which of the following is not an output device?

Scanner Printer Flat Screen Touch Screen

•

7. Which of the following devices have a limitation that we can only information to it but
cannot erase or modify it

Floppy Disk Hard Disk Tape Drive CDROM

•

8. No. of bits of IR___

a) 12 b) 8 c) 16 d) 24

9. Which technology is used in Compact disks?

Mechanical Electrical Electro Magnetic Laser

•

10. Which of the following storage devices can store maximum amount of data?
 Magneto Optic
Floppy Disk Hard Disk Compact Disk
Disk

11. Which of the following is the largest manufacturer of Hard Disk Drives?

IBM Segate Microsoft 3M

•

12. The memory location address are limited to

00000 to 9ffff(16) 00001 to 9ffff(16) 00010 to 9ffff(16) 10000 to 9ffff(16)

•

13. Data Bus is of

a) Unidirectional b) Bidirectional c) a or b d) None

14. The programs which are as permanent as hardware and stored in ROM is known as

Hardware Software Firmware ROMware

15. Memory is made up of

Large number of
Set of wires Set of circuits All of these
cells
16. Primary memory stores

Data alone Programs alone Results alone All of these

17. EPROM can be used for

Erasing and
Erasing the Reconstructing the
reconstructing the Duplicating ROM
contents of ROM contents of ROM
contents of ROM
18. Which device can understand difference between data & programs?

Input device Output device Memory Microprocessor

19. Logical shift left represents_____

a) R<- ashl R b) R € ShlR c) R € CilR d) Move

20. The contents of information are stored in

Memory data Memory address Memory access Memory arithmetic

register register register register
21. Represent -14 in signed magnitude representation.

a) 10001110 b) 01001110 c) 00101110 d) 00011110

22. Memory unit is one part of

 Central Processing
Input device Control unit Output device
Unit
23. Algorithm and Flow chart help us to

Know the memory Identify the base Direct the output Specify the problem
capacity of a number system to a printer completely and clearly
24. Which of the following is not a valid size of a Floppy Disk?

8" 5 1/4" 3 1/2" 5 1/2

25. A bus that connects components CPU, Memory, I/O
a) System Bus b) Data Bus c) Address Bus d) Control Bus

26. _______ is a program used to assign the specific addresses at which the object
code is to be loaded into memory.

a) Linker b) Compiler c) Locator d) Assembler

27. The electrical unit of clock rate is measured in

a) Hz b) Sec c) CPS d) None

28. Complements are used in digital computers for simplifying the ______ operaton.

a) Addition b) Multiplication c) Division d) Subtraction

29. First part of floating point representation represents a signed fixed point
number called___

a) Exponent b) Fraction c) Mantissa d) None

30. In the m*re expand m,r,e.

31. The third state of three state bus buffer is ___

a) logic 0 b) logic 1 c) high 1 medance state d) None

32. When the second part of an instruction code specifies an operand, the
instruction is said to an_____

a) immediate mode b) direct address c) indirect address d) None

33.. No. of bits of IR___

a) 12 b) 8 c) 16 d) 24

34. Reverse polish notation of (3*4)+(5*6) is _____

35. The transformation from the instruction code bits to an address in control
memory where the routine is located is referred to as a____

a) Mapping b) Branching c) Subroutine d) None

Essay questions

1.. Write about direct, indirect, register direct, register indirect, immediate, implicit,

relative, index, and base address mode of addressing. Why do we need so many

addressing modes? Is the instruction size influenced by the number of addressing

modes which a processor supports? State whether the number of addressing modes

will be more in RISC or CISC? [16]

Explain the terms computer architecture, computer organization and computer

design in a detailed fashion.
Design register selection circuit to select one of the four 4-bit registers content on

to bus. Give full explanation. [16]

What are functional units. Discuss on basic functional units of a computer.

Explain the following with applications for each:

(a) ROM

(b) PROM

(c) EPROM

(d) EEPROM. [4+4+4+4]

Explain in detail about the addressing modes with examples.

List various registers in a computer along with their purpose.

How do we reduce number of microinstructions. What are micro-subroutines?

Distinguish between error detection and correction codes. What do you understand

by odd parity and even parity?. What is odd function and even function?. To

calculate odd and even parity values which functions can be used? Calculate Odd

and even parity values for all hexadecimal digits 0-9 and A-F. [16]

Explain about stack organization used in processors. What do you understand

by register stack and memory stack? [10]

(b) Explain how X=(A+B)/(A-B) is evaluated in a stack based computer. [6]

How do you map micro-operation to a micro instruction address. [8]

(b) Hardwired control unit is faster than microprogammed control unit. Justify

this statement. [8]

4. (a) What is the use of fast multiplication circuits? Write about array multipliers.

[8]

(b) Multiply 10111 with 10011 using booths algorithm. [8]

(b) What are register transfer logic languages? Explain few RTL statement for

branching with their actual functioning. [8]

4. (a) Draw a flow chart which explains multiplication of two signed magnitude fixed

point numbers. [8]

(b) Multiply 10111 with 10011 with the above procedure given (a).

Show all the registers content for each step. [8]

(b) Explain time-shared common bus Organization. [5]

(c) Explain system bus structure for multiprocessors. [5]

Draw and explain about the instruction cycle state diagram.