Analog and Digital Electronics III-1. Digital Logic Integrated Circuits

Physics 201 Laboratory: Analog and Digital Electronics

III-1. Digital Logic Integrated Circuits

We use dual in-line package (DIP) integrated circuits (IC’s). You will have to get used to looking at a data sheet to figure out the pin configuration or to find the truth tables. Reference books are available and copies of the data sheets for some of the most common devices are provided as an appendix. The pins on an IC circuit are delicate. Keep each row straight and insert both rows simultaneously with gentle pressure. Do not pry the packages out of the breadboard. Rather, use the circuit removal tool that is provided. (It looks like a thin bent piece of metal.)

Obtain two 7404 ICs and one each of 7400, 7402, 7408 and 7432 and put them in your drawer. Note the 74xx number on each. Some of them have tiny circuit diagrams imprinted on them and others do not. In any event, once you remove an IC from a drawer, you are responsible for its identiﬁcation. Look brieﬂy at the “dual in-line package” circuit diagrams in the upper right hand corner of the data sheets and identify the functions with the truth tables in the accompanying notes.

1. Logic Inverter

Using a 7404 IC, build a LED logic inverter as shown in Fig. 1. Note the polarity of the diode and comment. Use a standard red LED. If it doesn’t light up when it should,

330 Ω

Vout

Vin

Figure 1: Logic Inverter. III-1. Digital Logic Integrated Circuits p. 2 turn it around. Show, by applying a logical ’1’ (i.e., 5 volts) and then a logical ’0’ (i.e., ground) to Vin that this is indeed an inverter (i.e., the diode lights when you apply zero volts and does not light when you apply 5 volts). Apply these voltages by running a wire from either ground or 5 V.

Now replace the ground with +5 V as shown in Figure 2 and repeat the observations. (Note that you must reverse the LED.)

+5 V

330 Ω

Vout

Vin

Figure 2: Logic Follower.

It is assumed from here on that you have a breadboard with digital logic capabilities.

Now you can exploit some of the features of a digital logic breadboard (DLB). (1) Connect one of the data switches output on the DLB to one of the logic indicators on the DLB. Use the data switch in both positions. (While you’re at it, check out the other logic indicators on the DLB.) Leave one lead in place so you know the output of the data switch. (2) Use the data switch output as the input to your inverter. (3) Remove both the 330 Ω resistor and the diode and connect the output of the inverter directly to a second logic indicator. (The logic indicator has its own internal resistor.)

2. Various Integrated Circuit Devices

Using data switches and the logic indicators on a DLB, test the truth tables of the 7408, 7432, 7400 and 7402 ICs (you have already done the 7404).

The instructor will ask you to put all ﬁve IC’s in a row such that everyone in the class uses the same order. The instructor may supply labels to help out.

Connect all the grounds togetherand to ground, and connect all the +5 V (VCC) together III-1. Digital Logic Integrated Circuits p. 3 and then to +5 V on the breadboard. Do not apply 5 volts directly to an input. Use the data switches. To test the output, use the logic indicators. The ports already include current-limiting resistors.

3. Simple IC Circuits

Use a NAND gate (7400) and an INVERTER (7404) to build an AND gate. Use the indicators on the DLB to check your results.

Use a NOR gate (7402) and in INVERTER (7404) to build an OR gate.

Build an “exclusive OR” gate. Work out the necessary truth tables ﬁrst and convince yourself that you need three gates. This is challenging.

The “exclusive OR” gate you have built is also a “one-bit adder.” That is, the output gives the 20 digit (two raised to zero) of the binary number corresponding to the sum of the binary numbers represented by the inputs. However, when both inputs are 1, the sum should be 1 + 1 = 10 (in binary), but your one-bit adder gives only the ‘0’ for the 20 digit. You need to also display the 21 digit—the “carry bit” (from “one plus one (binary) equals zero carry one”): 1 + 1 = 10. Can you create an output to display the carry bit?