# Lab 2 - Using Ligisim to simulate digital circuits

In this lab you will learn the basics of Digital Logic and operating the Digital Works Simulator.

### Documents

#### Step 1:

Review the Tutorial on Moodle here. Follow each step and try it for yourself.

#### Step 2:

Consider the following block diagram for a seven segment display, and it accompanying decoder circuit:

Note that there are 7 inputs to the 7-segment LED display. A one (1) on any input line lights the matching segment. A zero (0) input turns the segment off.

Thus a "4" can be displayed by putting:

0 -> a, d, e
1 -> b, c, f, g

Create a test circuit with a 7-segment LED display. and make it display a 4 using this (crude) method. Copy and paste the circuit into your lab report.

#### Step 3:

Consider the block diagram of the "BCD to 7 Segment Decoder". This is a circuit that takes binary values from 0 to 9, and sends the right signals to the Display to show the right number.

BCD stands for "Binary Coded Decimal".

Below is a table showing the decimal number, the binary version of the decimal number, ABCD, the corresponding inputs to the decoder, and abcdefg, the outputs needed by the decoder to light the LED correctly.

 # Binary A B C D a b c d e f g 0 0000 0 0 0 0 1 1 1 1 1 1 0 1 0001 0 0 0 1 0 2 0010 0 0 1 0 1 3 0011 0 0 1 1 0 4 0100 0 1 0 0 0 5 0101 0 1 0 1 0 6 0110 0 1 1 0 1 7 0111 0 1 1 1 0 8 1000 1 0 0 0 1 9 1001 1 0 0 1 0

Notice that the 0 inputs turns on all the segments BUT "g", which is the center segmentand must be off.

Also look down the "e" column. This shows all the times the "e" segment must be turned on, e.g. for 0, 2, 6, 8.

Fill in the rest of the table in your lab report.

#### Step 4:

Now consider a truth table constructed for the "a" segment:

 A B C D e 0 0 0 0 1 0 0 0 1 0 0 0 1 0 1 0 0 1 1 0 0 1 0 0 0 0 1 0 1 0 0 1 1 0 1 0 1 1 1 0 1 0 0 0 1 1 0 0 1 0

Now consider a circuit to implement the truth table:

Thus the circuit above can be connected to the appropriate segment.

Create and test this circuit.

#### Step 5:

Read the PDF "Designing a Macro" Take the Step for circuit and create a Macro for it. Then use it to control the 7-Segment display.

#### Step 6:

Now make a truth table, and a circuit for each of the other 6 segments. Turn each of these into a template. The inputs should all be connect to the same four inputs. Test out the circuit on all 10 values. Clip the circuit and paste into your Lab Report. Try to keep you circuits orderly and easy to read.

Topic attachments
I Attachment Action Size Date Who Comment
png 2_18_6_3_eng.png manage 1.8 K 2012-09-07 - 20:04 JimSkon LCDDecoder
GIF 7SegmentFinal.GIF manage 5.8 K 2012-09-07 - 20:07 JimSkon 7 Segment Final
GIF 7SegmentLEDFinal.GIF manage 6.6 K 2012-09-07 - 20:07 JimSkon 7 Segment LCD Final
pdf LogisimTechnicalManual.pdf manage 469.0 K 2012-09-07 - 20:11 JimSkon Logisim Manual
pdf logisim_tutorial.pdf manage 480.6 K 2012-09-07 - 20:12 JimSkon Logisim Technical Manual
Topic revision: r2 - 2012-09-10 - JimSkon

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