[time-nuts] GPDSO is working

[Chris Albertson]

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 <bob at 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 <alsopb at nc.rr.com>
> >To: Bob Stewart <bob at evoria.net>; Discussion of precise time and
> frequency measurement <time-nuts at 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 at 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