RS flip flop -- Replacing a NOR gate with an OR gate

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SUMMARY

The discussion centers on the implications of replacing a NOR gate with an OR gate in RS flip flops. It is established that this substitution leads to indeterminate outputs, specifically both Q and Q' yielding a value of 1 when both inputs are 0. The conversation emphasizes the necessity of an inverting function in bistable circuits, confirming that configurations using only two XOR gates or diode-only logic cannot achieve the desired bistable behavior.

PREREQUISITES
  • Understanding of RS flip flop functionality
  • Knowledge of NOR and OR gate operations
  • Familiarity with bistable circuits
  • Basic principles of digital logic design
NEXT STEPS
  • Research the design and operation of RS flip flops using NOR gates
  • Explore the role of inverting functions in bistable circuits
  • Investigate alternative bistable configurations using XOR gates
  • Study diode logic and its limitations in creating bistable circuits
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Electronics engineers, digital circuit designers, and students studying digital logic who seek to understand the behavior of RS flip flops and the importance of inverting functions in circuit design.

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In the RS flip flops using a NOR gate if we replace the NOR by an OR gate all the outputs will be indeterminate. Both outputs Q and Q' will every time yield 1. Can you explain how the inputs 0 and 0 will give 1 1 as output
 
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Try this,
Start with Set and Reset both being 1, and determine the outputs Q and Q-bar.
Then change either input ( or both ) to 0, and determine the outputs.

Start with Set and reset both being 0, and determine the outputs.
Change either input to a 1 ( or both ), and determine the outputs.

Repeat at your leisure.
 
Adding a diagram to help the OP:

https://commons.wikimedia.org/wiki/File:RS_Flip-flop_(NOR).svg

1586531521990.png
 
Afaik, there's a general principle that a bistable circuit needs some Inverting Function in there. I guess you could also make a bistable with XOR gates but I don't have a handy pencil at the moment.
 
sophiecentaur said:
I guess you could also make a bistable with XOR gates but I don't have a handy pencil at the moment.
Please find a pencil and see if it can be done with two 2-input XOR gates.
 
Dang - I knew I'd be called out on this one!
No chance with just two XOR gates. But any solution has to have an inverting logic function.
I don't think there would be a solution with Diode-only Logic either.
 
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