You have it 100% correct. The UT+ uses "positive" logic are the logic 1 is 5-volts but the RS-232 standard uses "negative" logic. I think the MAX232 does the conversion correctly EXCEPT if you read the RS-232 standards they use positive logic for the control signals.
On Fri, Jul 12, 2013 at 7:34 PM, Bob Stewart <b...@evoria.net> wrote: > Hi Brian, > > That's just strange. There are a whole lot of these MAX232 and MAX3232 > devices being sold. Hmm, I'm looking at the UT+ User's Guide, and it lists > the voltage levels as follows. These would imply that an inverter is > necessary, right? Could it be that someone programmed your PIC upside down > - i.e. using negative logic? > > TTL > 0 V to 0.8 V = logic 0 > 2.4 V to 5.0 V = logic 1 > RS-232 (reordered from manual to put logic 0 on top) > 5 V to 15 V = logic 0 > -5 V to -15 V = logic 1 > > Bob - AE6RV > > > > > >________________________________ > > From: Brian Alsop <als...@nc.rr.com> > >To: Bob Stewart <b...@evoria.net>; Discussion of precise time and > frequency measurement <time-nuts@febo.com> > >Sent: Friday, July 12, 2013 9:09 PM > >Subject: Re: [time-nuts] GPDSO is working > > > > > >Hi Bob, > > > >Here is my experience. I had a PIC that output RS232 at 0-5 volt > >levels. It actually worked with my computer directly. When I added a > >MAX 232 to make the levels something like -10/+10 volts. It didn't > >work. That's because the MAX232 inverts the polarity. Look at the data > >sheet, the level converters are clearly inverters. > > > >The fix in my case was to invert the RS232 stream output by the PIC and > >all was fine. > > > >I'm not sure exactly what you have but a scope sorts it out quickly. > > > >73 de Brian/K3KO > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.