Multisim and Ultiboard

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SN74121N One shot pulse generator help

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Hello,

 

I am having an issue where the SN74121N device is initially outputting a HIGH when I start the simulation on an oscope. Here is how I expect the circuit to function:

 

1. Toggle the PRI_PWR_ON1 switch from LOW to HIGH

2. Enable the flip flop U11 to output a pulse to SN74121N.

3. The SN74121N outputs a 68ms pulse (Note* you need to toggle the ~CRL on the flip flop to be able to to switch PRI_PWR_ON1 again)

 

Everything is working as normal except when I start the simulation, the SN74121 outputs HIGH even though I did not toggle the PRI_PWR_ON1 switch. I have already verified that the high pulse is not coming from devices before the SN74121N. So the high pulse is somehow preset to be high when I start the simulation. I have attached the simulation and a screenshot of the schematic. Any help will be much appreciated!

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