I'm trying to create a Program Counter
using some JK flip-flops.
I have two different way to do that:
-
Use some
74LS73
(dual JK flip-flop with clear): -
Use both
74LS10
(triple input NAND) and74LS00
(double input NAND):
Using the first integrated circuit will be easier, but this isn't the problem.
My doubt is about the Clear pin in 74LS73
: I know it will reset the flip-flop but also the combination J=0 and K=1 on a rising clock edge should do it…
So, what is the difference between the Clear pin and J=0, K=1, rising clock?
Best Answer
asynchronous vs. synchronous
asynchronous is easy for resetting the flip flop at power up. It does not require a clock to reset the flip flop.
synchronous is easy for changing the output to 0 during normal operation, it requires a clock to propagate to the output.
I could imagine if you want to build a counter, you want an easy way to reset all outputs to 0 at power up. The reset pin is ideal for that, because at power up without reset the outputs will be undefined/random. With the reset pin a power on reset doesn't require the input logic gates to get more complex.