Suppose that AB and CD are 2-bit unsigned binary numbers

(a) Find the truth table for the function F with 4 inputs A, B, C, D to satisfy the following condition

if AB >= CD, then F = 1, otherwise F = 0 enter image description here

(b) implement 8x1 multiplexer using 3x8 decoder and 3-state buffers

enter image description here

Am I right?

  • 1
    \$\begingroup\$ Isn't an 8x1 multimplexer supposed to have 8 data inputs? \$\endgroup\$ – Wouter van Ooijen Jun 18 '18 at 6:03
  • \$\begingroup\$ Yes, why......? \$\endgroup\$ – 김태후 Jun 18 '18 at 6:33
  • \$\begingroup\$ The drawing after (b) seems to answer subquestion (a), not (b). \$\endgroup\$ – Wouter van Ooijen Jun 18 '18 at 6:35
  • \$\begingroup\$ Thank you.. I've seen next (c) Design the logic diagram for the truth table of (a) using the circuit of (b). this is that.. \$\endgroup\$ – 김태후 Jun 18 '18 at 7:00
  • \$\begingroup\$ The output OR gate is not needed, only one gate is active , the outputs must be connected together \$\endgroup\$ – Dorian Jun 18 '18 at 12:27

a) You are wrong. Your truth table has several wrong entries, e.g. 0001 should be 0, not 1.

b) The drawn in OR gate though is wrong. With all but one input floating it is anyones guess what the output of an OR gate would be. Simply connect all the outputs together without further logic.

c) Your idea of connecting 1 and NOT D input signals to the 3-state buffers though is right. Except your bad truth table makes the result wrong. You also need 0 input for some.


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