simple CPU problem

Discussion in 'Homework Help' started by cgraider, May 29, 2012.

  1. cgraider

    Thread Starter New Member

    May 29, 2012
    hi everybody .
    my homework is make a simple CPU in proteus , I have it plan ,
    but there is a problem at the first stage :

    as u can see 4 leds are in the right and the third of them is on, and i draw another wire from it and used NOT gate SO IT SHOULD TURN OFF IN THE LEFT LED ,
    why doesnt it ? :|||||||||||||||||||:mad::mad::mad:
  2. absf

    Senior Member

    Dec 29, 2010
    The problem is obvious.....

    When the LED conducts, its terminal voltage would drop to a level which is seen by the simulator as logic Low even though the output from 74LS163 is High. In the real world, your LED would be long gone or the chip is toasted. But the simulator would tolerate this and still lights up your LEDs.:mad:

    Try to put a 470 ohm resistor in series with each LED and see what would happen.:D
    Last edited: Jun 6, 2012
  3. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    You need to pull the 74LS163 datasheet and review that. You are missing some connections as well as not having the current limiting resistors with each LED.
    Last edited: May 30, 2012