CSC270 Lab #3
CSC270 Lab #3
EXPERIMENT #1: THE 7408
Take a 7408 (or 74LS08, or 74S08) Integrated Circuit (IC) and put it on the breadboard part of the kit. Use the information shown in Figure 1 to help you wire the circuit. Always make sure that the circuit is connected to +5V through its pin 14, and to GND via its pin 7.
Connect pin 1 of the IC to Switch 1 (input A), pin 2 to Switch 2 (input B), and pin 3 to a logic indicator. Find the nature of the logic gate you are testing by activating all combinations of A and B.
| A | B | Output |
| 0 | 0 | |
| 0 | 1 | |
| 1 | 0 | |
| 1 | 1 |
Do the same for pin 4, 5 (inputs), and 6 (output). And for pins 13, 12 (inputs), and 11 (output). And for pins 10, 9 (inputs), and 8 (output).
Draw a diagram showing the contents of the integrated circuit (just show the gates inside the circuit).
EXPERIMENT #2: THE 7432
Swap the 7408 for a 7432, and repeat the same experiment (you only need to test the gate with Input Pins 1 and 2, and Ouput Pin 3. What logic function is implemented by the 7432?
| A | B | Output |
| 0 | 0 | |
| 0 | 1 | |
| 1 | 0 | |
| 1 | 1 |
EXPERIMENT #3: THE 7400
Swap the 7432 for a 7400, and repeat the same experiment. What logic function do you now have?
| A | B | Output |
| 0 | 0 | |
| 0 | 1 | |
| 1 | 0 | |
| 1 | 1 |
When you leave an input disconnected, what does the circuit see it as, a 1 or a 0?
EXPERIMENT #4: THE 7402
The 7402 is wired slightly differently from the other circuits. Connect its Pin 1 to a logic indicator, and Pins 2 and 3 to data switches. What is its logic function?
| A | B | Output |
| 0 | 0 | |
| 0 | 1 | |
| 1 | 0 | |
| 1 | 1 |
EXPERIMENT #5: THE 7404
Let's now test the 7404. Connect pins 1 and 3 to data switches, and pin 2 to a logic indicator. What is the logic function implemented by this circuit? (Hints: be careful with this one... There is a trick here...)
| A | B | Output |
| 0 | 0 | |
| 0 | 1 | |
| 1 | 0 | |
| 1 | 1 |
EXPERIMENT #6: Implement a 3-input Priority Encoder
Implement the 3-input priority encoder seen in class today. We generated the circuit for the INT signal, but not for the C0 and C1 signals.
Create the truth table for C0 and C1.
| m | f | h | C0 | C1 |
| 0 | 0 | 0 | ||
| 0 | 0 | 1 | ||
| 0 | 1 | 0 | ||
| 0 | 1 | 1 | ||
| 1 | 0 | 0 | ||
| 1 | 0 | 1 | ||
| 1 | 1 | 0 | ||
| 1 | 1 | 1 |
Now that you have the truth tables, express C0 and C1 in their minterm canonical forms.
Once you have the minterm canonical forms of C0 and of C1, use the theorems and postulates of boolean algebra (see Mano, Page 41) to simplify their expression.
x+0 = x x.1 = x x+x' = 1 x.x' = 0 x+x = x x.x = x x+1 = 1 x.0 = 0 (x')' = x x+y = y+x xy = yx x+(y+z) = (x+y) + z
x(yz) = (xy)z x(y+z) = xy + xz x + yz = (x+y)(x+z) (x+y)' = x'.y' (x.y)' = x'+y' x+xy = x x(x+y)= x
Once you are at this stage, get and/or print a set of data sheets for the following circuits:
Draw a clean version of the whole circuit for INT, C0 and C1.
Identify the circuits numbers (e.g. 7408) corresponding to your logic gates,
and write these numbers INSIDE the gates in your diagram.
Then identify which
gate in the circuit you will be using, and write the pin-numbers of the gate
next to the inputs and outputs. The figure of the AND-gate shows an example of how
one would label an AND gate, assuming that we use the first AND of a 7408, with
inputs on pins 1 and 2, and output on pin 3.
When you are done labeling all the gates in this fashion, put the ICs you need on the breadboard, and turn the power off. Connect the circuits power and gnd pins to +5 and GND.
Then add wires between the gates, making the connections that you have shown on your diagram. As you add wires, highlight or redraw in bold the corresponding lines in your logic diagram, so that you can easily see which connections are made and which ones are left. Make sure you use three data switches for the mouse, floppy, and hard-disk signals, and that you connect the INT, C0 and C1 signals to logic indicators.
Turn the power on, and test your circuit. Does it prioritize the inputs? Were you able to implement everything with just one integrated circuit?
Same implementation, but now you can only use NOR gates...
Circuit Library
You may find these two electronic libraries of integrated circuits useful when wiring up your circuits: