Due date: October 17, 2001
Department of Computer
and
Mathematical Sciences
CS 3402
Digital Logic
Laboratory
7
Lab 7: BCD-to-Seven-Segment Display Controller
Objectives:
The goal for this lab is to use LogicWorksTM to design a circuit that maps a 4-bit BCD digit to
the signals that control a seven-segment display using a decoder.
Background:
Medium scale integration (MSI) devices can be used to implement digital logic circuits instead
of using primitive gates. MSI devices are decoders, multiplexers, demultiplexers, PLAs. Some
MSI devices can be implemented directly from the truth table such as multiplexers.
In this lab, we will make use of decoders to implement seven-segment display. Seven-segment
display, as shown in Figure 1, is a device to display digits from 0 to 9.
dot
g
a
Figure 1: Seven-Segment Display in LogicworksTM
The display element contains seven light-emitting diodes (LEDs). When the appropriate LED
control line is asserted, the associated LED segment lights. The seven segments are controlled
independently; there is no limit to the number of segments that could be illuminated at the same
time. There is a seven-segment display device in LogicWorksTM as shown in figure 1.
Figure 2: Configuration of Segments of SevenSegment Display
Figure 3: Configuration of the Pins Associated with
LED Segments in LogicworksTM
Figure 2 and 3 illustrates the configuration of the pins associated with LED segments.
Fall 2001, Lab 07,
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For example, to make a seven-segment display to show digit 7, pins C0, C1 and C2 (pins a, b,
and c in LogicWorksTM) are asserted to make corresponding LED segments lit and displayed 7 as
shown in Figure 4.
Figure 4: Seven-Segment Display Displays Digits Form 0 to 9
Task 1: Implementation of Decoders
The objective of this task is to implement decoders for BCD to seven-segment display.
Activity 1 Construct a truth table for a BCD-to-seven-segment display controller. For example,
the BCD input 0111 will make the seven-segment display show 7.
Fall 2001, Lab 07,
3
Activity 2 Use LogicWorksTM to construct the circuit diagrams from the truth table in Activity 1
using one decoder 74154 and hex keyboard without strobe as input. Then test your circuit and
demonstrate your working circuit to the instructor. Illustrate your circuit diagram.
Activity 3 Use 74138 3:8 decoders in place of the 74154 in Activity 2. Test your circuit.
Illustrate your circuit diagram.