Using D Flip-flops to create a certain sequence pattern

william chan

Hi,

How to create the sequence 001, 010, 100, 111, repeat, using four D flip flops?
I tried using a variation of a reverse ring counter but not successful.
Any tips or pointers would be very appreciated.

Phil Pilgrim (PhiPi)

Do your D flip-flops have /preset and /clear inputs (e.g. like 74HC74)? If so, it can be done with three D f/fs.

-Phil

william chan

Yes, my D Flip Flops have preset and clear inputs.
How to do it with three flip flops?

Phil Pilgrim (PhiPi)

This should do the trick (no presets or clears needed, it turns out):



-Phil

william chan

You are a genius !
Thanks a million.

yeti

A 2 bit shift register and a 2 bit clock divider sharing one DFF, very nice!

macrobeak

OK Phil, so how did you solve that so quickly?
I was going to refer William to online simulators but you smashed it first!

Phil Pilgrim (PhiPi)

macrobeak wrote:

OK Phil, so how did you solve that so quickly?

By arranging the desired outputs in a column and recognizing familiar patterns.

-Phil

yeti

I saw the the pattern after doubling the table to see 2 periods.

Mickster

william chan wrote: »

You are a genius !

Ya got that right....examples like this make me feel like an intruder in an exclusive club.

Beau Schwabe

Phil,

Of course this does not go without a "Golf Challenge"

Note: A and C should be swapped in the attached diagram

Phil Pilgrim (PhiPi)

Ha! Clever!

-Phil

yeti

Using an XOR when the question was to use DFFs only?
Golfing the POTUS way?
Missing the hole and/or bending the rules?

But a nice solution for a related modified question.
;-)

Beau Schwabe

Since when have you known me to play by the rules? - lol

Besides technically, the OP stated four DFF, and Phils solution used three. I didn't sense that we were limited to only DFF's.

Attached is another solution using one DFF and some discrete components that form an RTL XOR gate