D flip flop

Thread Starter


Joined Mar 1, 2008

How can i use a D flip flop 7474, to operate as a "memory" device?
example: a user store some password into a system(using d flipflop). now, if he enter the password correctly, he have access to the system, if he enter 3 times wrong, its lock.

for the 7474, clk signal must be connect to the clk input of chip only.

any suggestion?

The flipflop has a PR n CLR, should i make use of that?


Joined Feb 24, 2006
At one bit per FF you're going to need quite a few of them. You would be better off using a microcontroller for that purpose. If you still insist on a discrete logic implementation then I would suggest a gate array.


Joined Feb 11, 2007
a bit can store 2 states.
a byte stores 256 states.
The ascii system is at least 7 bits long, typically 8.

So to store 1 character, you need at least 4 7474's. you could use 1 74xxx73 (8-bit latch/flip-flop), but the best way to go is to use a microcontroller.