Uh oh.... sounds like I need to dig deeper, huh? I've got a 1uF tantalum directly across pin 7 to gnd, but that's it. maybe this thing just can't drive enuf to remain stable? I'm going to try a MAX232 (but they were out o' stock which is the ONLY reason I went with the '233!). Thanks all for the inputs! I'll let ya know whazzup! 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.