sequential circuit using D flip-flops

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fm_com_28

Joined: 02 Feb 2006
Posts: 158
Helped: 5
Location: Fayoum, Egypt

03 Oct 2006 15:38 74xx00 flip flop

Dear,
I want to Design a sequential circuit with two D flip-flops A and B, and one input x. When x=0, he sate of the circuit remains the same. When x=1, the circuit goes through the start transitions from 00 to 101 to 11 to 10 back to 00, and repeats.

tronix

Joined: 06 Jul 2006
Posts: 121
Helped: 6

04 Oct 2006 9:12 sequential circuit having two d flip flops

I suggest you to consult the book
'Digital Logic and Computer Design' by Morris Mano.
or 'Digital Design' by the same author.
These should be available in the e-book section of the forum.

Regards
tronix

nikhilele

Joined: 11 Jan 2006
Posts: 543
Helped: 22
Location: Bangalore India

06 Oct 2006 6:30 gray code using d flip flop

i am not able to understand your transistions.
please make it more clear

"transitions from 00 to 101 to 11 to 10 back to 00, and repeats"

what is 101 doing in two bit sequential ckt.

i think u want 00,10,11,10,00
is this right sequence....

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fm_com_28

Joined: 02 Feb 2006
Posts: 158
Helped: 5
Location: Fayoum, Egypt

06 Oct 2006 13:41 design of sequential circuit using d flip flop

lambtron

Joined: 02 Nov 2005
Posts: 256
Helped: 26
Location: Portland, OR

06 Oct 2006 15:50 design of seqentional circuit using d flip flop

Simple. Here's the next-state equations for AB:

A = ( A and not X ) or ( B and X )

B = ( B and not X ) or ( X and not A )

jonw0224

Joined: 22 Nov 2004
Posts: 199
Helped: 28
Location: USA

08 Oct 2006 17:28 design d flip flop using sequential circuit

A simple challenge (just for fun):

Implement the circuit (described above) with standard logic chips (no PLD or uP). I'll donate 20 points to the person using the fewest chips who submits a working schematic to this topic. Assume a clock signal is available.

-jonathan

dindeds

Joined: 11 Aug 2006
Posts: 130
Helped: 9

11 Oct 2006 3:30 flip flop ckt

Nah.. you can't do that with 2 D-Flip flop without help of several others logic gates in between them.
But then I'd rather get my 12F675 to do it in a jiffy at a fraction of the cost!

nikhilele

Joined: 11 Jan 2006
Posts: 543
Helped: 22
Location: Bangalore India

12 Oct 2006 8:36 using d flip flop make jk flip flop

i think this can be done by JK flip flop.

Added after 1 minutes:

using jk will simplfy the task
I will also try with D flip flop

jonw0224

Joined: 22 Nov 2004
Posts: 199
Helped: 28
Location: USA

12 Oct 2006 13:38 circuit using flipflop

dindreds,

I don't understand your "fraction of the costs". I do not think you are talking about money. The 12F675 is 1.70 or so.

The cost of a discrete logic chip is 0.25 to 0.40. I'll even add 0.15 per chip for the additional PCB space for say 0.55 per chip.

Someone can easily (using a trick or two) implement this with three chips (2 NANDS, 74XX00, and a Dual D flip flop, 74XX74). I'm sure there are some cool implementations with JK flip flops as well. Anyway, a three chip implementation costs 1.65 at the most.

Others may realize that this circuit is fairly simple and the logic is built (but maybe hidden) into other discrete chips. Multiplexers are good ways to implement logic for 1 to 3 variables (and some even have flip flops built into the outputs -- hmm, state machine on a chip?).

Still others may be able to do creative, out of the box, things with counters or shift registers as long has they can handle reset conditions. To make it easier to use these chips, I'd allow someone to use a reset line. The line can be active low or active high, I don't care.

There may be a one chip implementation out there, I know that there are *multiple* two chip implementations. In which case the costs are 1.10 at most. A single chip implementation would cost a third of the microcontroller (and not be much bigger) and perform much faster (if speed is a consideration).

The point here is to have fun trying. I am just looking at the problem more generally, pose the next step to the original question so to speak. Someone may get some benefit out of it (or the results) or atleast enjoy working out a neat simple problem. There are people wasting time on suduko and other puzzles for enjoyment. These types of problems (puzzles) are what I enjoy so I waste my time on them Smile

-jonathan

beta0

Joined: 24 Nov 2003
Posts: 120
Helped: 7

12 Oct 2006 18:12 sequential circuit using d- flip flop

fm_com_28 wrote:

Hi fm_com_28, what you need exactly is nothing but a gray code counter. Very Happy

10kangstroms

Joined: 04 Oct 2004
Posts: 83
Helped: 14

13 Oct 2006 4:54 fm_com_28

beta0 wrote:

fm_com_28 wrote:

Hi fm_com_28, what you need exactly is nothing but a gray code counter. Very Happy

Also known as a Johnson counter. You can make it with 2 D flipflops (one package, such as 74xx74) and nothing else.
This reminds me of a funny story. A couple of years ago, an engineer at work showed me the new 5-stage, 10-state counter he had "invented". I said, "Bill, that's a Johnson counter". The funny thing was, his last name is Johnson. Johnson counters have been around for decades.