I am very new to digital logic, and have just started to learn about feedback in circuits. The basic example of an OR gate with its output connected to one of its inputs creates a circuit that seems to behave like an SR latch without a reset function (i.e. once it receives an input it will output high indefinitely) so I am wondering if the following modification to this circuit would allow it to function as a latch, and why the standard topology using two NOR gates is preferred.
Would this circuit work like an SR latch?
yes it works well as Q with positive logic input.
Why is it better to use two NOR gates?
- It is minimal and R is faster AND gives both outputs Q & Q*.
- This uses negative logic on inputs.
- Using 2 NAND gates also gives identical results.
The main advantage of your circuit solution is that it is your small and maybe first "invention"... and you understand very well the basic idea behind the elementary latch...
Really, NOR and NAND implementations are minimalistic and tidy. But there is even simpler implementation of a latch as two cross-coupled inverters (1-input gate)... and this is the most elementary memory cell used in SRAM. It would be interesting and useful for you to figure out how it is driven... what are its inputs and outputs.
Nobody ever implements individual SR latches in circuit design except within an integrated circuit.
Within an IC the basic active element is a transistor (bipolar or FET) and all such devices act as inverters with one or more inputs to create a NAND or NOR gate as the minimum element.
Creating a non-inverting gate such as an AND or OR gate requires additional devices to invert the signal at the input or output of an inverting gate.
Your SR latch would function but would require more transistors than one made of basic inverting gates. It would also be slower and use more power.