Ma. Isabel Berdin
Sasan Simkani
Mary Angela Yu
PS 141 C Lab Report #3
Group 8 January 23, 2002
What input does our 0110 block box detect?
Like the other ICs our block box, which consists of a NAND (7400) and a NOR (7402) chip, gets its input from the output of other ICs. In our experiment, the block box’s inputs are from the outputs of the 7490 chip. Output pins 9 and 8 of the 7490 are connected to the two-input NAND gates. Also output pins 12 and 11 of the 7490 are connected to the two-input NOR gate.
We designed the circuit using the NAND and NOR chips in such a way where the input combination 0110 is only accepted. That is the block box will only send an output of logic 1 if it receives the input combination 0110. Otherwise, the block box will send an output of logic 0 if it receives any other input combinations.
Here is a diagram of the combination of four two-input NAND and of one two-input NOR gate we used to assure that only the input combination 0110 is accepted.
What output does it give?
The block box will give an output of logic 1 if it detects an input combination 0110. For any other input combinations detected, the block box will give an output of logic 0.
How is the block box connected to the 7490?
Aside from the connections of the output pins of the 7490 to the input pins of the block box, there is also a connection between an output pin of the block box to the reset pins of the 7490, which are pin 2 and 3.
What does it do to the 7490?
Due to the apparent connections of the two ICs, whenever the output of the block box is 1, then the pins 2 and 3 of the 7490 would also become 1. If you’ll remember from the previous lab report, whenever pins 2 and 3 of the 7490 is 1 or "high", then 7490 would reset its count to 0. The effect of this is that the 7490 would only be counting up to 6. This is since every time the 7490 reaches the count 6, the block box will send logic 1 to the reset pins 2 and 3. Thus the 7490 will reset its count to 0. Therefore, since the 7490 is connected to the 7442 (which is connected to all the LEDs), then only 6 of the 10 LEDs would light.
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