[time-nuts] GPDSO is working
Bob Stewart
bob at evoria.net
Sat Jul 13 02:34:40 UTC 2013
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
>
>
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