multisim intermittent digital logic problem

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super7800

Joined Apr 3, 2019
30


the above circuit is part of what i have done for my first year eeng digital logic final project. the circuit works by the user inputting a number on the pushbutton pad, and loading said number into the selected shift register bank (max 4 digits), and whenever the +,-,equal button is pressed it should switch banks. that circuit is at the moment only opperated by the select switch to select the banks. i have also designed a circuit so that when the "backspace" button is pressed it will shift the selected shift register bank 4 bits left, thus deleting the most recent number. this circuit might be part of the problem.

my problem is one of the hardest to debug-an intermittent one. i launch multisim and the circuit works flawlessly, and never crashes roughly 25% of the time. the other times i have to close out multisim and open it again, and this sometimes fixes it, sometimes does'nt. i have narrowed the problem down to the clock circuit, and even more specifically believe the problem to be with the two lines highlighted above. i have tried everything i could think of. when it does fail, it always does so at Tran: 0.013s mark. once it makes it past that its fine and will not crash no matter what during that specific simulation. once i rerun chances are that its failing again. the 555 timer is running at 60hz.

Here is a link to download my simulation file for any of you who have multisim (14.1 is my version):
http://www.mediafire.com/file/399fu97f8s9sz4z/multisim_simulations_calculator_2.ZIP/file

please let me know if you see any obvious problems or know of any solutions or suggestions, or need further clarification on how the circuit specifically opperates. is this simply a problem with multisim? thanks.
 
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