I need help confirming some hunches. I'm trying to figure out what type of circuit this is:
Any ideas?
Also, I think the logic expression for this is:
D = (A AND B) OR (NOT(B) AND C)
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2 Answers
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There are only two intermediate signals, so it's relatively easy to break down. We'll call the left input to the bottom OR gate X and the right input Y.
I'm going to use some shorthand here - NOT = !, AND = &, OR = |.
X = A & B Y = !B & C
Those two lead into the OR gate that produces D:
D = (A & B) | (!B & C)
Which is the result you came up with, so you are correct.
One application of this logic circuit is to act as a selector:
- When
Bis asserted, thenAis output onD, andCis ignored. - When
Bis de-asserted, thenCis output onD, andAis ignored.
answered Feb 28, 2010 at 3:18
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1\$\begingroup\$ Yeah, that definitely looks like a 2-1 multiplexer. It passes A or C to the output, depending on the value of B. \$\endgroup\$– ajs410Apr 29, 2010 at 21:25
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3\$\begingroup\$ It's a multiplexer, but it's not a hazard-free one. Even if A and C are true, a rising or falling edge may generate a glitch on the output. A hazard-free multiplexer would include "A and C" as an extra term on the output "or" gate. \$\endgroup\$– supercatJun 16, 2011 at 2:12
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Its a 2:1 multiplexer, the select input being B. A and C are inputs, D is the output
