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Two, Two-Input DTL AOI Gate

Introduction

Because we haven't changed the inputs to our DTL inverters when forming a NOR gate, it is possible for us to combine the DL AND function with the DTL NOR function and obtain an AND-NOR combination. Since an AND-OR sequence is very often in demand, this combination is useful in some applications.

In addition, it is a very easy function to obtain; we need only add the input diodes for the AND functions, just as we did for the three-input NAND gate in a previous experiment.

In this experiment, you will expand your NOR gate to perform an AND-NOR function. This combination is also known commonly as an AND-OR-Invert function.



DTL AND-OR-Invert (AOI) gate.

Schematic Diagram

The DTL AND-OR-Invert gate simply adds input diodes to each transistor in the basic NOR gate. Thus, we have DL AND gates connected to a DTL NOR gate. This arrangement should work, in view of our success with the DTL NAND gate. Here, we are simply combining AND and NOR functions in a single gate.

Of course, this function is not always what is wanted in a given application. However, where such a function is desirable, this combination serves the need in a very compact and efficient form.



Parts List

To construct and test the DTL AND-OR-Invert gate on your breadboard, you will need the DTL NOR gate from the previous experiment plus the following experimental parts:



Constructing the Circuit

Select an area on your breadboard socket that is clear of other circuits. You'll need two adjacent sets of five bus contacts for this project. Then refer to the image and text below and install the parts as shown.



Circuit Assembly

Start assembly procedure

Beginning the Assembly

You should still have the DTL NOR gate in position on your breadboard socket, as shown in the assembly diagram to the right. If you did not perform the earlier DTL experiments or if you removed the components, go back and assemble that circuit now. You'll need it in place to complete this experiment.

Click on the `Start' button below to begin adding the additional components for this experiment.

1N914 Signal Diode

You may have a 1N914 diode left over from prior experiments, which is already formed to a lead spacing of 0.4". If not, locate a 1N914 diode and form its leads to a spacing of 0.4". Install this diode in the location shown in the assembly diagram. Be sure to observe the indicated orientation of the diode.

Click on the image of the diode you just installed to continue.

1N914 Signal Diode

If you have a second 1N914 diode left over from prior experiments, which is already formed to a lead spacing of 0.4", go ahead and use it here. If not, locate a 1N914 diode and form its leads to a spacing of 0.4". Install this diode in the location shown in the assembly diagram. Be sure to observe the indicated orientation of the diode.

Again, click on the image of the diode you just installed to continue.

3" Orange Jumper

Locate a 3" orange jumper among the parts left over from previous experiments. If necessary, cut a 3" length of orange hookup wire and remove ¼" of insulation from each end. Connect this jumper from S1 to the point shown in the assembly diagram.

Click on the image of this jumper to the right to continue.

6" Orange Jumper

Locate a 6" orange jumper among the parts left over from previous experiments. If you don't have one, cut a 6" length of orange hookup wire and remove ¼" of insulation from each end. Connect this jumper from S1 to the point shown in the assembly diagram.

As before, click on the image of this jumper to the right to continue.

Assembly Complete

This completes the construction of your experimental circuit. Check your assembly carefully against the figure to the right, and correct any errors you might find. Then, proceed with the experiment on the next part of this page.

Restart assembly procedure


Performing the Experiment

Set switches S0, S1, S6, and S7 all to logic 0. Then, turn on power to your experimental circuit, and record the output as indicated by L0 in the first row of the table to the right. Continue to set your logic switches to each possible combination of four input signals, and record the circuit output for each possible combination of inputs. What is the logic function performed by this circuit?

When you have entered your results for all 16 input combinations, turn off power and then compare your results with the discussion below.

Inputs Output
S7 S6 S1 S0 L0
0 0 0 0
0 0 0 1
0 0 1 0
0 0 1 1
0 1 0 0
0 1 0 1
0 1 1 0
0 1 1 1
1 0 0 0
1 0 0 1
1 0 1 0
1 0 1 1
1 1 0 0
1 1 0 1
1 1 1 0
1 1 1 1


Discussion

In performing this experiment, you should have found that switches S0 and S1 operate as a pair, while S6 and S7 operate as another pair. If both switches in either pair were at logic 1, L0 was forced to a logic 0 state. However, so long as one switch in each pair was at logic 0, the output shown by L0 was a logic 1.

Thus, this circuit first performs a logical AND between the switches of each pair, then performs a NOR operation between those two results. That is exactly what we were looking for from this circuit.

This is the final experiment with DTL gates. Make sure power is off; then remove all experimental components from the right hand side of your breadboard socket and set them aside. You will need many of them for your next set of experiments.


Prev: 2-input DTL NOR Gate Next: Transistor-Transistor Logic

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