74154 4 line to 16 line decoder

In summary, the conversation discusses designing a circuitboard using a 74154 4 line to 16 line decoder to output a high when the 4 bit binary is greater than 12 and a low when it is less than or equal to 12. The design involves using a NAND gate for inputs 13-15 and a NOR gate for inputs 0-12, with both outputs being connected to an XOR gate. However, there is uncertainty about how the solution achieves the desired output.
  • #1
ravenprp
2,891
0
Hi.. my HW question reads:

Design a circuitboard based on a 74154 4 line to 16 line decoder that will output a HIGH henever the 4 bit binary is greater than 12 and output a low when it is less than 12 or equal to 12.

http://pdf1.alldatasheet.com/datasheet-pdf/view/7826/NSC/74154.html

I have the IC drawn on my paper, and what I have done is for the inputs from 13-15, I have it going to an NAND gate.

so if one of those inputs is an active LOW input, then once gates 13, 14, 15 go through the NAND with the values 0, 1, 1, (respectively), it will output a "1" or "HIGH"... Now, for gates 0 - 12... I'm using a NOR gate.

Now, I connect the NAND gate and the NOR gate into a XOR gate.Brief recap: gates 13-15 go into a NAND. That output goes into one input for an XOR. Then gates 0-12 go into a NOR. Then that output goes into one input for the same XOR as above.
 
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  • #2
I'm not sure that I understand your solution. The outputs of the 4:16 demux represent the count of the input lines, right? So if you want to output a 0 when the input count is 12 or more, what can you put on lines 12-15 to output a 0 if any input is a 1, and output a 0 otherwise?
 
  • #3


The second input for the XOR is a constant "1" input. This will ensure that the output of the XOR will be a "1" or "HIGH" only when the input from gates 13-15 is a "1" and the input from gates 0-12 is a "0". This satisfies the condition of the output being "HIGH" only when the 4 bit binary is greater than 12.

For the output to be "LOW" when the 4 bit binary is less than or equal to 12, we can simply use an inverter on the output of the XOR gate. This will result in the output being "LOW" when the XOR output is "1" and "HIGH" when the XOR output is "0", fulfilling the desired condition.

Overall, this circuit design utilizes the NAND and NOR gates to create a condition where the output will be "HIGH" only when the input is greater than 12 and "LOW" when the input is less than or equal to 12. The XOR gate acts as a comparator to compare the inputs and produce the desired output.
 

Related to 74154 4 line to 16 line decoder

What is a 74154 4 line to 16 line decoder?

A 74154 4 line to 16 line decoder is an integrated circuit that takes in a 4-bit binary input and selects one of 16 possible outputs based on the input. It is commonly used in digital electronics to decode and select specific signals.

How does a 74154 decoder work?

The 74154 decoder works by using a combination of AND gates and inverters to produce a unique output for each possible input combination. The 4 input lines represent the 4 bits of the binary input, while the 16 output lines correspond to the 16 possible output combinations.

What are the applications of a 74154 decoder?

A 74154 decoder has many applications in digital electronics, such as in address decoding, data selection, and control signal generation. It is commonly used in microprocessors, memory chips, and other digital systems where multiple signals need to be selected based on a binary input.

What are the advantages of using a 74154 decoder?

One major advantage of using a 74154 decoder is its compact size and simplicity. It can replace multiple logic gates and reduce the complexity of a circuit. It also has a fast response time and can handle a wide range of input and output voltages.

Are there any limitations to using a 74154 decoder?

One limitation of a 74154 decoder is that it can only handle 4-bit inputs, limiting the number of possible inputs to 16. It also has a limited number of available outputs, which may not be sufficient for some complex systems. Additionally, it is not suitable for analog signals and can only process digital inputs.

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