Simulation Output From IC 74LS247N Is Inverted in Multisim

Updated Oct 2, 2024

Reported In

Software

  • Multisim

Issue Details

I am designing circuits using IC 74LS247N in Multisim but the output from the IC is inverted based on the datasheet of the IC, why?
01.PNG

Solution

The truth table output of this model is inverted which causes the issue above. Follow the below steps to modify the truth table:
  1. Double-click the IC in Multisim.
  2. Select the Value tab and choose Edit model.
Image_2024-04-22_14-00-52.png
  1. Replace the model truth table with the below truth table and select the Change component.
+; LT' RBI' D C B A BI/RBO'  A B C D E F G
+   H   H   L L L L    H     L L L L L L H
+   H   H   L L L H    H     H L L H H H H
+   H   H   L L H L    H     L L H L L H L
+   H   H   L L H H    H     L L L L H H L
+   H   H   L H L L    H     H L L H H L L
+   H   H   L H L H    H     L H L L H L L
+   H   H   L H H L    H     H H L L L L L
+   H   H   L H H H    H     L L L H H H H
+   H   H   H L L L    H     L L L L L L L
+   H   H   H L L H    H     L L L H H L L
+   H   H   H L H L    H     H H H L L H L
+   H   H   H L H H    H     H H L L H H L
+   H   H   H H L L    H     H L H H H L L
+   H   H   H H L H    H     L H H L H L L
+   H   H   H H H L    H     H H H L L L L
+   H   H   H H H H    H     H H H H H H H
+   X   X   X X X X    L     H H H H H H H
+   H   L   L L L L    L     H H H H H H H
+   L   X   X X X X    H     L L L L L L L
+   H   X   X X X X    H     L L L L L L L
Image_2024-04-22_14-03-37.png

 

Additional Information

Besides editing the model truth table of that IC, there are two more alternatives you may consider:
  1. Design the circuit with the 74LS248N/D instead of the 74LS247N/D
  2. Design the circuit with the 74LS47N instead of the 74LS247N/D
  3. Use transistors and resistors to invert outputs A-G

Related Links

External Link: BCD-to-Seven-Segment Decoders/Drivers datasheet

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