How does one implement the following function with these tools provided

digital-logicinputinvertermultiplexer

Suppose I have a function defined as follows, such that it is expressed in POS form,
with the product of the following max terms of 4 variables (A,B,C,D):

0,3,4,7,9,10,12,15

and I only have a 4 to 1 multiplexer, one inverter, and one 2-input gate of my choice.

What would be the approach going about solving a question like this? In addition, what
would be the "correct" 2-input gate to use in this situation?

My idea:

Crunch out all possible combinations of inputs then take all possible gates possible for those particular inputs:

(A,B)
(B,C)

etc.

However I feel that takes too long and a rather cumbersome approach to take.

Best Answer

the question can be solved in another way... As, POS of F(A,B,C,D)=0,3,4,7,9,10,12,15.

convert to SOP.

SOP of F(A,B,C,D)=1,2,5,6,8,11,13,14.

Now when u write down all the minterms you can group two terms together like keeping A'B' common A'B'CD'+A'B'C'D i.e.sop(2,1) to be equal to A'B'(C exor D) similarly others will also group up to form terms of xnor

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Related Solutions

Electronic – the minimum number of NOR gates needed to implement a 2-input multiplexer

You can build the mux with 4 NOR gates, too. It doesn't require extra inverters on the inputs and outputs, if that's what you were doing. Note that the sense of the "select" input is inverted, so you need to swap the "A" and "B" inputs to compensate.

Electronic – How to debug red signals in ModelSIM

Nice to see a proper testbench and code that actually matches the question for a change...

There are two easy ways for a signal to be corrupted:

drive it from several signal sources
don't drive it from any

Now A11 remains 'U' throughout, suggesting it has no driver. While A1 alternates between valid and 'X' invalid values, suggesting it has more than one driver.

With that in mind, review your code where you drive A1 and A11.

You'll laugh...

To expand on the "how to debug" part of the question : having aroused a suspicion that signals were not driven from the expected sources, you could use Modelsim's "drivers" command to list the drivers on a signal. If you had written slightly more verbose VHDL, and labelled each process, that would get you the same answer without having to review your code...

e.g.

Drive_A1 : process
begin
   a1 <= '0' ; wait for 4ns;
   ... etc

Best Answer

Related Solutions

Electronic – the minimum number of NOR gates needed to implement a 2-input multiplexer

Electronic – How to debug red signals in ModelSIM

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