[time-nuts] GPDSO is working

[Bob Stewart]

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
>
>