LDCO Practical Oral Questions

Q. Questions
No
1 What is Gray Code?
2 Explain the Weighted & Non-Weighted Number System.
3 Which code can be used in Kmap?
4 What do you mean by Reflective & Self Complement
Code?
5 Explain the applications of Gray Code?
6 What is Universal Gate?
7 Design Ex-OR gate from universal gate.
8 List down all the ICs used in Digital Laboratory.
9 Describe Do Not care combination.
10 What is Boolean algebra?
11 Why do we use Boolean algebra?
12 What is invalid BCD?

S.
QUESTION
No
1 Write different BCD addition rules.
Discuss and designcircuit to detect invalid BCD number and
2
implement using NAND gate only.
A combinational circuit has four inputs (A,B,C,D), which
represent a binary coded-decimal digit. The circuit has two
groups of four outputs -S,T,U,V(MSB digit) and W,X,Y,Z.(LSB
3 digit). Each group represents a BCD digit. The output digits
represent a decimal number which is five times the input
number. Illustrate the minimum expression for all the
outputs?
Draw and describe the working principle of a two-digit BCD
4
adder.
5 Why do we add 6 i.e. (0110)2 for BCD correction?
6 Write a short note on five-bit BCD codes?
Solve arithmetic operation indicated below. Follow signed
7 bit notation: i. 001110 + 110010 ii. 101011 - 100110. b)
Explain the importance of gray code?
8 Solve (3250 - 72532)10 using 10's complement?
In a 32 bit computer, what are the maximum and minimum
9 possible binary numbers? Convert these into maximum and
minimum possible positive decimal numbers?
Convert the octal numbers into binary, decimal, BCD and
10 Hexadecimal numbers(3600)octal,(1200)octal,(0200)octal,
(0777)octal.
Convert the decimal numbers into binary, BCD and
11
Hexadecimal numbers (3600)d, (1200)d, (0200)d, (0777)d.
Suppose you have a cheque for RS.10000/-.what is the
12 number system used? Define base system used and what
are the weights of the digits 1,0,0,0,0 and 0 now?
 S.
QUESTION
No
1 Define Multiplexer, Demultiplexer.
2 Define Encoder, Decoder
3 What is the role of select lines?
4 Explain the real life applications of multiplexer.
Develop down the relation between MUX inputs & select
5
lines.
6 How many MUX’s are present in IC 74LS138.
7 What is the name of IC 74LS138?

What is the relation between Input lines & output lines in

Q. Questions
No
1 What is the name of IC 7490 & 74191?
2 Identify Whether 7490 is Synchronous or Asynchronous?
3 How many flip-flops are present in IC 7490 & 74191.
4 What is Biquinary Counter ?
5 What is Truncated Counter ?
6 Identify the nature of circuit. (is Synchronous or
Asynchronous)

Experiment No. 6:- Design of Arithmetic Logic Unit:

Theory for Design of ALU

ALU or Arithmetic Logical Unit is a digital circuit to do arithmetic operations like addition,
subtraction,division, multiplication and logical oparations like and, or, xor, nand, nor etc. A simple
block diagram of a 4 bit ALU for operations and,or,xor and Add is shown here :
The 4-bit ALU block is combined using 4 1-bit ALU block

Design Issues :
The circuit functionality of a 1 bit ALU is shown here, depending upon the control signal S1 and S0
the circuit operates as follows:
for Control signal S1 = 0 , S0 = 0, the output is A And B,

for Control signal S1 = 0 , S0 = 1, the output is A Or B,

for Control signal S1 = 1 , S0 = 0, the output is A Xor B,

for Control signal S1 = 1 , S0 = 1, the output is A Add B.

The truth table for 16-bit ALU with capabilities similar to 74181 is shown here:
Required functionality of ALU (inputs and outputs are active high)
Mode Select Fn for active HIGH operands
Inputs Logic Arithmetic (note 2)
S3 S2 S1 S0 (M = H) (M = L) (Cn=L)
L L L L A' A
L L L H A'+B' A+B
L L H L A'B A+B'
L L H H Logic 0 minus 1
L H L L (AB)' A plus AB'
L H L H B' (A + B) plus AB'
L H H L A⊕B A minus B minus 1
L H H H AB' AB minus 1
H L L L A'+B A plus AB
H L L H (A ⊕ B)' A plus B
 H L H L B (A + B') plus AB
H L H H AB AB minus 1
H H L L Logic 1 A plus A (Note 1)
H H L H A+B' (A + B) plus A
H H H L A+B (A + B') plus A
H H H H A A minus 1
The L denotes the logic low and H denotes logic high.

Objective
Objective of 4 bit arithmetic logic unit (with AND, OR, XOR, ADD operation):
1. Understanding behaviour of arithmetic logic unit from working module and the module
designed by the student as part of the experiment
2. Designing an arithmetic logic unit for given parameter
Examining behaviour of arithmetic logic unit for the working module and module designed by the student
as part of the experiment (refer to the circuit diagram):
Loading data in the arithmetic logic unit (refer to procedure tab for further detail and experiment
manual for pin numbers):
• load the two input numbers as:
• A(A3 A2 A1 A0): A3=1, A2=1, A1=0, A0=0
• B(B3 B2 B1 B0): B3=1, B2=0, B1=0, B0=1
• carry in(C0)=0
examining the AND behaviour:
• load data in select input as:
• S1=0, S0=0 `
• check output:
• F3=1, F2=0, F1=0, F0=0
• cout=0 `
examining the OR behaviour:
• load data in select input as:
• S1=0, S0=1 `
• check output:
• F3=1, F2=1, F1=0, F0=1
• cout=0 `
examining the XOR behaviour:
• load data in select input as:
• S1=1, S0=0 `
• check output:
• F3=0, F2=1, F1=0, F0=1
• cout=0 `
examining the ADD behaviour:
• load data in select input as:
 • S1=1, S0=1 `
• check output:
• F3=0, F2=1, F1=0, F0=1
• cout=1 `
Recommended learning activities for the experiment: Leaning activities are designed in two
stages, a basic stage and an advanced stage. Accomplishment of each stage can be self-evaluated
through the given set of quiz questions consisting of multiple type and subjective type questions. In
the basic stage, it is recommended to perform the experiment firstly, on the given encapsulated
working module, secondly, on the module designed by the student, having gone through the theory,
objective and procuder. By performing the experiment on the working module, students can only
observe the input-output behavior. Where as, performing experiments on the designed module,
students can do circuit analysis, error analysis in addition with the input-output behavior. It is
recommended to perform the experiments following the given guideline to check behavior and test
plans along with their own circuit analysis. Then students are recommended to move on to the
advanced stage. The advanced stage includes the accomplishment of the given assignments which
will provide deeper understanding of the topic with innovative circuit design experience. At any
time, students can mature their knowledge base by further reading the references provided for the
experiment.
• color configuration of wire for 5 valued logic supported by the simulator:
• if value is UNKNOWN, wire color= maroon
• if value is TRUE, wire color= blue
• if value is FALSE, wire color= black
• if value is HI IMPEDENCE, wire color= green
• if value is INVALID, wire color= orange
likewise the 16 bit arithmetic logic unit can be designed and tested
• by cascading 4 bit ALUs only the carry will propagate to the next level for ADD operation

Test plan :
1. Set inputs 0101 and 0011 and check output for all possible select input combinations.
2. Set any two 16-bit number and check output for all possible select input combinations.
Use Display units for checking output. Try to use minimum number of components to build. The
pin configuration of the canned components are shown when mouse hovered over a component.

Assignment Statements :
1. Design a 4 bit ALU comprising only the AND, OR, XOR and Add operations.
2. Design a 16-bit ALU with capabilities similar to 74181
Procedure
Design of ALU:
Procedure to perform the experiment: Design of 4 bit ALU
1. Start the simulator as directed. This simulator supports 5-valued logic.
2. To design the circuit we need 4 1-bit ALU, 11 Bit switch (to give input,which will toggle its
value with a double click), 5 Bit displays (for seeing output), wires.
3. The pin configuration of a component is shown whenever the mouse is hovered on any
canned component of the palette. Pin numbering starts from 1 and from the bottom left
corner (indicating with the circle) and increases anticlockwise.
4. For 1-bit ALU input A0 is in pin-9,B0 is in pin-10, C0 is in pin-11 (this is input carry), for
selection of operation, S0 is in pin-12, S1 is in pin-13, output F is in pin-8 and output carry
is pin-7
5. Click on the 1-bit ALU component (in the Other Component drawer in the pallet) and then
click on the position of the editor window where you want to add the component (no drag
and drop, simple click will serve the purpose), likewise add 3 more 1-bit ALU (from the
Other Component drawer in the pallet), 11 Bit switches and 5 Bit Displays (from Display
and Input drawer of the pallet, if it is not seen scroll down in the drawer), 3 digital display
and 1 bit Displays (from Display and Input drawer of the pallet, if it is not seen scroll down
in the drawer)
6. To connect any two components select the Connection menu of Palette, and then click on the
Source terminal and click on the target terminal. According to the circuit diagram connect all
the components. Connect the Bit switches with the inputs and Bit displays component with
the outputs. After the connection is over click the selection tool in the pallete.
7. See the output, in the screenshot diagram we have given the value of S1 S0=11 which will
perform add operation and two number input as A0 A1 A2 A3=0010 and B0 B1 B2
B3=0100 so get output F0 F1 F2 F3=0110 as sum and 0 as carry which is indeed an add
operation.you can also use many other combination of different values and check the result.
The operations are implemented using the truth table for 4 bit ALU given in the theory.
Circuit diagram of 4 bit ALU:

Screenshot of Design of 4 bit ALU:

Components :
To build any 4 bit ALU, we need :
1. AND gate, OR gate, XOR gate
2. Full Adder,
3. 4-to-1 MUX
4. Wires to connect.
In case of counters the number of flip-flops depends on the number of different states in the counter.
Experiment
Design of ALU :
General guideline to use the simulator for performing the experiment:
• Start the simulator as directed. For more detail please refer to the manual for using the
simulator
• The simulator supports 5-valued logic
• To add the logic components to the editor or canvas (where you build the circuit) select
any component and click on the position of the canvas where you want to add the
component
• The pin configuration is shown when you select the component and press the 'show
pinconfig' button in the left toolbar or whenever the mouse is hovered on any canned
component of palette
• To connect any two components select the connection tool of palette, and then click on
the source terminal and then click on the the target terminal
• To move any component select the component using the selection tool and drag the
component to the desired position
• To give a toggle input to the circuit, use 'Bit Switch' which will toggle its value with a
double click
• Use 'Bit Display' component to see any single bit value. 'Digital Display' will show the
output in digital format
• undo/redo, delete, zoom in/zoom out, and other functionalities have been given in the top
toolbar for ease of circuit building
• Use start/stop clock pulse to start or stop the clock input of the circuit. Clock period can
be set from the given 'set clock' button in the left toolbar
• Use 'plot graph' button to see input-output wave forms
• Users can save their circuits with .logic extension and reuse them
• After building the circuit press the simulate button in the top toolbar to get the
output
• If the circuit contains a clock pulse input, then the 'start clock' button will start the
simulation of the whole circuit. Then there is no need to again press the 'simulate'
button