Brandeis University Physics 29a
Spring 2016 Kevan Hashemi

Lab 10: Combinatorial Logic

Logic Chips: Data sheets for the SN7400N quad two-input NAND gate is on the 29A web page. The "SN" means "Texas Instruments". Any other manufacturer code can preceed the 7400 and the functionality is the same. The 74S00 and 74LS00 are faster and lower-power versions of the 7400 respectively. You can use them too.

Construction Principles: Use the breadboard power supply, it's more convenient, and perfectly adequate for logic circuits. Use wires no longer than necessary to connect two points. Plan the arrangement of your logic chips to reduce the number of crossing wires. Use black for 0 V and red for +5 V. Use the columns of contacts for power. Remember to connect the upper columns to the lower colums with a wire link.

Part 1: Construct your own two-input NOR gate using diodes, bipolar transistors, and resistors. Connect its two inputs to switches and its one output to one of the logic level indicator lamps on your breadboard. These indicator lamps are LEDs in series with resistors. Demonstrate your NOR gate to an instructor.

Part 2: Consider the following truth table. Write down the boolean equations that express the truth table logic. Manipulate these equations until you arrive at an expression that can be implemented with two-input NAND gates alone. Note that you may construct an inverter out of a NAND gate by connecting its two inputs together.


You will find it easier to build the circuit if you try to reduce the number of NAND gates it requires. In this case, the minimum number of gates required to impement the function is five. But you may build the circuit with as many gates as you like, so long as it implements the truth table above.