I have come across Flip-Flop memory elements & it seems really cool, So far i have only did Set, Reset Using Flip Flop, I am eager to know that Is there a way to create a 2 bit / 4bit memory element using Flip Flop? I mean using NAND/NOR gates?
Electronic – way to create a 2 bit / 4bit memory element using Flip Flop
circuit analysisdigital-logic
Related Solutions
You can build the mux with 4 NOR gates, too. It doesn't require extra inverters on the inputs and outputs, if that's what you were doing. Note that the sense of the "select" input is inverted, so you need to swap the "A" and "B" inputs to compensate.
Assume ideal logic gates (no propagation delay) like this (image from wikipedia):
We know that the output of NOR gate is 1 if and only if both inputs are 0; and 0 otherwise.
When S = 1, Q = 1 and therefore \$\bar{Q} = 0\$; when R = 1, Q = 0 and \$\bar{Q} = 1\$.
But if you set both R and S to 1 we have that Q = 0 and \$\bar{Q} = 0\$ at the same time. This contradicts the relation \$Q = \bar{Q}\$. In the real world one of the gates will reach the 1 state first and the result will be unpredictable.
For the NAND-based RS flip-flop the same can be shown when R = S = 0, by writing the logic equations appropriately.
Best Answer
You need to understand that a D type flip flop is a 1 bit memory element. When you give it a set signal it'll store its D input and will output it from the Q output on the fallowing cycles, until the set bit is raised again or the reset bit is set.
So, by putting 2 or more flip-flops together, with the same clock, set and reset inputs what you get is an n bit register, or n bit memory unit.
A diagram for a 2 bit register from flip-flops:
This is of course a volatile memory, meaning it'll lose its value once power supply is cut off.
Also, while this is the way registers are made, for example in the cpu, this is not the way that cache and RAM memories are made.