BCD to Seven-Segment Decoder
You are likely familiar - very familiar - with the idea of a seven-segment indicator for representing decimal numbers. Each segment of a seven-segment display is a small light-emitting diode (LED) or liquid-crystal display (LCD), and - as is shown below - a decimal number is indicated by lighting a particular combination of the LED's or LCD's elements:
Bindary-coded-decimal (BCD) is a common way of encoding decimal numbers with 4 binary bits as shown below:
Your job for this lab is to design and test a circuit to convert a 4-bit BCD signal into a 7-bit control signal according to the following figure and table:
Notice that the truth-table corresponds to a seven-segment device whose display elements are active low. That is, each element will be active when its corresponding input is '0'.
Enter the schematic for your circuit into the MAX+plusII CAD system, then simulate your circuit to verify that it works. Your waveform simulation should test all 10 binary number codes.
Hint: When entering a circuit schematic in sum-of-products or product-of-sums form, you may find it convenient to form a 'bus' of all inputs and their complements. For sum-of-products you would then have a layer of and-gates followed by a layer of or-gates. Likewise, for product-of-sums, you would have a layer of or-gates followed by a layer of and-gates. As an example, consider the 3-input, 2-output circuit with the following product-of-sums description:
a = (b1 + ~b2)(~b0 + ~b1 + b2)
A convenient way to enter this schematic is shown below. Keep in mind that your design will be different in that you will likely implement a circuit in sum-of-products form.
Your laboratory report should illustrate your circuit design and document the testing you performed to verify its function. Your simulation should produce a waveform file similar to the one shown below.
Your completed report, including the initialized Instructor Verification Sheet, is due at the beginning of your next lab meeting.
Remember to save all files associated with this project. You will program a device and test this circuit in two weeks.
Copyright © 2000
Department of Electrical and Computer Engineering
Michigan Technological University
Timothy J. Schulz