# The Analysis of a Set-Reset Flip-flop

## Keywords:

elearning, digital logic, set-reset## Abstract

**The Set State**

Consider the circuit shown. If the input R is at logic level “0” (R = 0) and input S is at logic level “1” (S = 1), the NAND gate *Y* has at least one of its inputs at logic “0” therefore, its output Q must be at a logic level “1” (NAND Gate principles). Output Q is also fed back to input “A” and so both inputs to NAND gate *X* are at logic level “1”, and therefore its output Q must be at logic level “0”. Again NAND gate principals. If the reset input R changes state and goes HIGH to logic “1” with S remaining HIGH also at logic level “1”, NAND gate *Y* inputs are now R = “1” and B = “0”. Since one of its inputs is still at logic level “0” the output at Q still remains HIGH at logic level “1” and there is no change of state. Therefore, the flip-flop circuit is said to be “Latched” or “Set” with Q = “1” and Q = “0”.

**Reset State**

In this second stable state, Q is at logic level “0”, (not Q = “0”) its inverse output at Q is at logic level “1”, (Q = “1”), and is given by R = “1” and S = “0”. As gate *X* has one of its inputs at logic “0” its output Q must equal logic level “1” (again NAND gate principles). Output Q is fed back to input “B”, so both inputs to NAND gate *Y* are at logic “1”, therefore, Q = “0”. If the set input, S now changes state to logic “1” with input R remaining at logic “1”, output Q still remains LOW at logic level “0” and there is no change of state. Therefore, the flip-flop circuits “Reset” state has also been latched and we can define this “set/reset” action in the following truth table.

## References

Manual Pengguna, (2022). Aplikasi Pendidikan dan Reka Bentuk Elektronik Digital (S. Widyarto, Ed. & Trans.; 1st ed.). International Community Forum (ICF).

https://www.digitalelectronicsdeeds.com/

{3} https://www.electronics-tutorials.ws/sequential/seq_1.html

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## How to Cite

*Proceedings of the Informatics Conference*,

*8*(17). Retrieved from https://ojs.journals.unisel.edu.my/index.php/icf/article/view/236