[SOLVED] proteus SN74LS181 simulation problem

Discussion in 'Electronics Resources' started by gomi, Jan 20, 2019.

  1. gomi

    Thread Starter New Member

    Jan 20, 2019
    5
    0
    I am trying to make work 181 ALU. I do not claim to know anything. I am very amateur. I tried to connect everything correctly but I can not see leds working for a simple operation example -> 1+1=2. What am I doing wrong here ?
    upload_2019-1-20_22-15-30.png
     
  2. bertus

    Administrator

    Apr 5, 2008
    19,024
    3,771
    Hello,

    You have the pins 7 and 8 floating.

    74181_fucntiontable.png

    Pin 8 is the M input and pin 7 is the CN input.

    Bertus
     
    gomi likes this.
  3. MrChips

    Moderator

    Oct 2, 2009
    17,773
    5,547
    74LS181 is a 5V device. B1 = 12V is too high.

    All of your inputs are floating. With 7kΩ resistors in series your circuit is not going to work.
    You need to guarantee valid LOW and HIGH logic levels on all inputs.

    You should never connect LEDs directly to logic outputs. Use an LED driver circuit to power the LED.
     
  4. gomi

    Thread Starter New Member

    Jan 20, 2019
    5
    0
    That works now I think I got correct results with sum operation like: 3+3 = 6. That was not working before as ground and VCC pins are not given and I tried to use normal battery. Resistance is now 2k.
    upload_2019-1-21_1-10-47.png
     
  5. Papabravo

    Expert

    Feb 24, 2006
    11,868
    2,523
    You don't want to use pulldown resistors with LSTTL. The inputs source current and will cause the voltage on those resistors to creep up toward the threshold
     
  6. gomi

    Thread Starter New Member

    Jan 20, 2019
    5
    0
    I corrected that now.
     
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