Newsgroups: comp.robotics
Path: brunix!news.Brown.EDU!agate!howland.reston.ans.net!cs.utexas.edu!utnut!cannon.ecf!leebr
From: leebr@ecf.toronto.edu (LEE  BRIAN)
Subject: Re: FLIP-FLOP....
Message-ID: <CKMz3z.Mu6@ecf.toronto.edu>
Sender: news@ecf.toronto.edu (News Administrator)
Organization: University of Toronto, Engineering Computing Facility
References: <CKK8Ht.CFG@ecf.toronto.edu> <2ipn7d$pb6@vixen.cso.uiuc.edu>
Date: Thu, 3 Feb 1994 06:52:46 GMT
Lines: 34

>]Right, and please give me any advice if you know how to do that.
>]I mean I need the Q and Q' be the same state in order the control
>]the braking and 'free-wheel' motion of the H-Bridge motor control.
>
>Somewhere amonst all the flamage and namecalling, I posted that you can
>indeed make Q and Q' high at the same time by making /PRE and /CLR active
>low at the same time.  All the wiseguys can sit in the corner with their
>textbooks and state diagrams.  "Real world" integrated circuits are much
>more susceptible to brute force than state tables are.  This info is available
>in any CMOS or TTL databook.  Remind me not to ask for a job anywhere they
>have flamers who think you can't put both outputs of a ff in the same state. 

hmmm... when I first read your reply, I remembered some things I
looked over when I was designing some F/Fs.  I think this is really
implementation dependent, and it probabably depends on which
signal is asserted first, etc.  Anyway, a quote from TI's TTL Data Book:

	* the output levels in this configuration are not
	guaranteed to meet the minimum levels for VOH if
	the lows at Preset and Clear are near VIL maximum...

anyway, I suggest redesigning the circuit and forget using the
F/F in some really weird way.

later,
bjl

(---> Yes, you should hire UofT engineers!)

-- 
+=[O]=============================================================[<]=[>]=+
| Brian Jonathan Lee (aka "hojo")    | "Bleh!"                            |
|    leebr@skule.ecf.toronto.edu     | "Got'er, done'er, done'er, got'er" |
|    leebr@ugsparc0.eecg.toronto.edu | "Evil thy name is NETREK!"         |
