Hi Ken, Good point about ESD... I suppose there's no easy way to deduce if that was the issue; to my knowledge, I've never caused myself any such grief with my "handling methods", so my tendency is to put higher probabilities elsewhere. But I suppose it might be time to move the Van deGraaf generator out of the lab! ( :^) just kidding!). Jim ----- Original Message ----- From: "Ken Pergola" To: Sent: Saturday, August 02, 2003 10:56 AM Subject: Re: [PIC] RS232 w/ MAX233 question... > Hi Jim, > > Please be careful here Jim... > > Don't be too quick to blame the manufacturer -- you never know if the chip > was damaged by ESD. > By no means am I'm saying that ESD damage was the problem, but it is > something to always be mindful about. > From some of the training I've received, I've learned that ESD can cause > latent failures -- enough to make you pull your hair out! > > Glad you made some progress finding the problem -- good luck with your > project. > > Best regards, > > Ken Pergola > > > -----Original Message----- > From: pic microcontroller discussion list > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jim Tellier > Sent: Saturday, August 02, 2003 11:01 AM > To: PICLIST@MITVMA.MIT.EDU > Subject: Re: [PIC] RS232 w/ MAX233 question... > > > Bob, thanks for the heads up confirming my suspicions... as I see it right > now, even with 1uF tantalum + .1uF right on pin 7, with NO xmit activity on > its input, the '233s RS232 output driver "breaks into song" all by itself a > few seconds after power-up. :^( NOW.... for the interesting discovery! I > said earlier that I'd swapped out the '233, and saw same symptoms. Just > now, I swapped it again, but this time I yanked a '233 that I knew to be > working out of another project (fortunate use of sockets!) ... and damn if > it WORKS! The two that I'd been using initially were Maxim "engineering > samples" (wonder if that's a synonym for "rejects"?!). Methinks it's time > for a few words to Maxim. Anyway, Caveat Emptor, E Pluribus Unum, Trust > No One, and Keep on Truckin'! > Jim > > ----- Original Message ----- > From: "Bob Axtell" > To: > Sent: Friday, August 01, 2003 8:52 PM > Subject: Re: [PIC] RS232 w/ MAX233 question... > > > > I hate to add to your woes, but I have to tell you that that's the one > that > > also sings out RF real bad, tried filtering & caps (worked OK then) but > > finally had to scrap their use by going overbudget on 4 sets of filters (I > > couldn't get it to pass radiation tests). 5 more caps was cheaper than 4 > > filters. Yep, that's the very one. As Yosemite Sam used to say, "that's > mah > > story and ah'ma stickin' to it." You might have to drop back to less > > exotic (and cheaper) part... > > > > In all fairness to Maxim, the problem seems to be that most folks don't > > bypass the Max233 with a tantalum cap large enough (i.e. very low delivery > > impedance) to get the current it needs instantaneously and a 0.1uF RF > > killer to quash the RF it generates, both across the line right at the > > MAX233. We did all of that stuff, didn't help. > > > > Sometimes, when something is too good to be true, it isn't. I know 10 > > engineers personally that all went thru that expensive learning session. > > > > --Bob > > > > At 08:25 PM 8/1/2003 -0700, you wrote: > > >The '233 doesn't require external caps. There are no bad/broken > > >connections: like I said, it works -- when it starts up. Tried another > > >chip, same behavior. It does "seem" like an RC time-constant effect, in > > >that the time required for the symptom to surface after power-up > decreases > > >as I increase the frequency of powering-up the circuit. I see no > > >misbehavior on the PIC side of things - i.e. the inputs to the MAX233 are > > >solid. Mystifry me, man! > > >Jim > > >----- Original Message ----- > > >From: "Patrick J" > > >To: > > >Sent: Friday, August 01, 2003 6:40 PM > > >Subject: Re: [PIC] RS232 w/ MAX233 question... > > > > > > > > > > ok, sounds to me like your caps is either wrong value/bad solder/or > > >broken? > > > > tried another chip? > > > > > > > > > TXSTA/TRMT = HIGH before sending), and the output of the '233 turns > to > > > > s*** > > > > > after a few seconds! (the P-P amplitude of the waveform drops to > about > > > > 6v, > > > > > and it looks like it's broken into oscillation). The input to the > '233 > > >is > > > > > much difference. Hmm? > > > > > Jim > > > > > > > > -- > > > > http://www.piclist.com hint: The list server can filter out subtopics > > > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > >-- > > >http://www.piclist.com hint: The list server can filter out subtopics > > >(like ads or off topics) for you. See http://www.piclist.com/#topics > > > > --------------- > > NOTICE > > > > 1. This account can accept email & attachments up to 10M in size. > > 2. Federal Monitors: At request of client, some attachments are encrypted. > > Please DO NOT delay traffic; please reply with credentials for password. > > -------------- > > > > -- > > http://www.piclist.com hint: The list server can filter out subtopics > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.