1.3.1 Logic Gates

Computer Science 2210
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Topic: 1.3.1 Logic gates
Other Questions:
In questions 1 to 6, produce truth tables from the given logic networks. Remember that if there are
TWO inputs then there will be four (22) possible outputs and if there are THREE inputs there will be
eight (23) possible outputs.
i.e.
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Questions 7 to 10 require both the logic network to be created and also the truth table. The truth
table can be derived from the logic network, but also from the problem. This is a check that the
logic network actually represents the original problem.
(7) A computer will only operate if three switches P, S and T are correctly set. An output signal
(X = 1) will occur if P and S are both ON or if P is OFF and S and T are ON. Design a logic network
and draw the truth table for this network.
(8) A traffic signal system will only operate if it receives an output signal (D = 1). This can only
occur if:
either (a) signal A is red (i.e. A = 0)
or (b) signal A is green (i.e. A = 1) and signals B and C are both red (i.e. B and C are both 0)
Design a logic network and draw a truth table for the above system.
(9) A chemical plant gives out a warning signal (W = 1) when the process goes wrong. A logic
network is used to provide input and to decide whether or not W = 1.
A warning signal (W = 1) will be generated if

either (a) Chemical Rate < 10 m3/s
or (b) Temperature > 87 C and Concentration > 2 moles
or (c) Chemical rate = 10 m3/s and Temperature > 87 C
Draw a logic network and truth table to show all the possible situations when the warning signal
could be received.
(10) A power station has a safety system based on three inputs to a logic network. A warning
signal (S = 1) is produced when certain conditions occur based on these 3 inputs:
A warning signal (S = 1) will be generated if:

either (a) Temperature > 120C and Cooling Water < 100 l/hr
or (b) Temperature < 120C and (Pressure > 10 bar or Cooling Water < 100 l/hr)
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Draw a logic network and truth table to show all the possible situations when the warning signal
could be received.
Past Papers Questions:
May/June 2011. P11

10 (a) Two logic gates are the AND gate and the OR gate. Complete the truth tables for these
two gates:
(b) Complete the truth table for the following logic circuit:
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May/June 2011. P12
11 (a) (i) Complete the truth table for the following logic circuit:
(ii) Which single logic gate has the SAME function as the above logic circuit? [1]
Oct/Nov 2011. P11
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Oct/Nov 2011. P13
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May/June 2012. P11
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May/June 2012. P12
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Oct/Nov 2012. P13
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May/June 2013. P11
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May/June 2013. P12
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Oct/Nov 2013. P12
10(a) (i) Complete the truth table for the following logic circuit which is made up of NORgates
only.
[2]
(ii) What single logic gate has the same function as the above circuit? [1]
……………………………………………………………………………………………………………
…………………………………………………………………………………………………………...
(b) Complete the truth table for the following logic circuit.
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Oct/Nov 2013. P13
11 (a) Draw the logic circuit for the following logic statement:
X = 1 if [ A is NOT 1 AND B is 1 ] AND [ B is 1 OR C is 1 ]
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(b) Complete the truth table for the above logic circuit.
May/June 2014. P11

7 (a) Draw the logic circuit for the logic statement:
X = 1 if (L is NOT 1 AND F = 1) OR (F is NOT 1 AND A is 1)
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(b) Complete the truth table for the above system.
May/June 2014. P12

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17 (a) Complete the truth table for the following logic circuit:
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(b) Write the logic statement to describe the following logic circuit:
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Past Papers Questions:
A Level
Section 1.10: Logic Gates

May/June 2011. P11
6. Complete the table for this circuit of logic gates.
[6]
May/June 2011. P12

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[6]
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May/June 2011. P13
[6]
Oct/NOV 2011. P11

9 (a) Complete the table to show the outputs for the possible inputs to this circuit.
[2]
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(b) Complete the table to show the outputs for the possible inputs to this circuit.
[4]
Oct/NOV 2011. P12

9 (a) Complete the table to show the outputs for the possible inputs to this
circuit.
[5]
(b) State a possible use for this circuit in a processor. [1]
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Oct/NOV 2011. P13
9 (a) Complete the table to show the outputs for the possible inputs to this
circuit.
[2]
(b) Complete the table to show the outputs for the possible inputs to this
circuit.
[4]
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May/June 2012. P11/12
9 (a) Complete the truth table to show the output from the logic gate
shown.
[2]
(b) Complete the truth table to show the outputs from the logic circuit
shown.
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[4]
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May/June 2012. P13
9 (a) Complete the truth table to show the output from the logic gate
shown. [2]
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(b) Complete the truth table to show the outputs from the logic circuit
shown.
[4]
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Oct/NOV 2012. P11
10 (a) (i) Complete the truth table for this logic circuit. [1]
(ii) State a single logic gate which would have the same final outcome as this
pair of logic gates. [1]
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[4]
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Oct/NOV 2012. P12
10 (a) (i) Complete the truth table for this logic circuit. [1]
(ii) State a single logic gate which would have the same final outcome as his
pair of logic gates. [1]
(b) Complete the truth table for this logic circuit.
[4]
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Oct/NOV 2012. P13
10 (a) (i) Complete the truth table for this logic circuit.
[1]
(ii) State a single logic gate which would have the same final outcome as this
pair oflogic gates. [1]
(b) Complete the truth table for this logic circuit.
[4]
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May/June 2013. P11/P12

9 (a) Draw the logic circuit corresponding to the following logic statement:
X = 1 IF (A is 1 AND B is 1) OR (B is 1 OR C is NOT 1)
[4]
(b) Complete the truth table for the above logic statement:
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[4]
May/June 2013. P13

6 (a) Draw the logic circuit corresponding to the following logic statement:
X = 1 IF ( (A is NOT 1 AND B is 1) OR (B is 1 AND C is 1) ) OR (C is 1)
[5]
(b) Complete the truth table for the above logic statement:
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[4]
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Oct/NOV 2013. P12
10 (a) (i) Complete the truth table for the following logic circuit which is made up of
NORgates only.
[2]
(ii) What single logic gate has the same function as the above circuit? [1]
(b) Complete the truth table for the following logic circuit.
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[4]
Oct/NOV 2013. P13

11 (a) Draw the logic circuit for the following logic statement:
X = 1 if [ A is NOT 1 AND B is 1 ] AND [ B is 1 OR C is 1 ]
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[4]
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(b) Complete the truth table for the above logic circuit.
[4]
May/June 2014. P11/12
8 A car has an engine management system (EMS). The EMS outputs the following signals.
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(a) (i) Draw a logic circuit for the following fault condition:
All three signals (A = 1, B = 1 and C = 1) indicate a fault. The driver is warned to stop
the engine – output X = 1.
(ii) Draw a logic circuit for the fault condition:

Either (A = 1 and B = 1) or (B = 1 and C = 1) indicate a fault. The driver is warned that
the engine needs a service – output Y = 1.
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(iii) Draw a logic circuit for the fault condition:
Either A = 1 or B = 1 or C = 1 indicate a fault. A red warning light shows up on the
dashboard – output Z = 1.
May/June 2014. P13
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(b) Draw a logic circuit corresponding to the following logic statement:
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May/June 2015. P11
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(b) Draw a logic circuit which corresponds to the following logic statement:
X = 1 if ((A is NOT 1 OR B is 1) AND C is 1) OR (B is NOT 1 AND C is 1)
(c) Write a logic statement which corresponds to the following logic circuit:
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May/June 2015. P12
6 A gas fire has a safety circuit made up of logic gates. It generates an alarm (X = 1) in response
to certain conditions.
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The output X = 1 is generated under the following conditions:
gas pressure is correct AND carbon monoxide level is too high
OR
carbon monoxide level is correct AND gas leak is detected
(a) Draw a logic circuit for this safety system.
(b) Complete the truth table for the safety system.
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(c) Complete the truth table for the XOR gate:
[1]
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1.3.1 Logic Gates

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What are logic gates and how are they used?

What are logic gates and how are they used?

What is a truth table and how is it used?

What is a truth table and how is it used?

Computer Science 2210

Topical Past Papers

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

A warning signal (W = 1) will be generated if

A warning signal (S = 1) will be generated if:

Topic: 1.3.1 Logic gates

Past Papers Questions:

May/June 2011. P11

Topic: 1.3.1 Logic gates

Oct/Nov 2011. P11

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Oct/Nov 2013. P13

Topic: 1.3.1 Logic gates

May/June 2014. P11

Topic: 1.3.1 Logic gates

(b) Complete the truth table for the above system.

May/June 2014. P12

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Section 1.10: Logic Gates

May/June 2011. P12

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

6. Complete the table for this circuit of logic gates.

Oct/NOV 2011. P11

Topic: 1.3.1 Logic gates

Oct/NOV 2011. P12

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

Topic: 1.3.1 Logic gates

(b) Complete the truth table for this logic circuit.

Topic: 1.3.1 Logic gates