Re: [gpsd-users] gpsd:WARN: PPS TIOCMIWAIT returns unchanged state, ppsmonitor sleeps 10

[Gary E. Miller]

Yo Hamish!

On Wed, 3 Jul 2013 05:20:25 -0700 (PDT)
Hamish <address@hidden> wrote:

> >>  > According to the manual it is TIA-232-F which according to
> >>  > wikipedia
> 
> >>  > is true rs232.  
> Gary:
> >>  Put a voltmeter or a scope on it.  I can count on one hand the
> >> number of people I have met that have actually read that spec.
> >> Unless it explicitly says +/-12V you do not know.
> Charles:
> > I have also read that alleged spec. Everything is considered
> > "advisory", including the notion that the people who wrote it could
> > communicate at all. Nope, a scope or VM is the only way to go.
> > Check it with the cable plugged in and unplugged.
> 
> fwiw, and I'm not sure which spec you're talking about here so please
> ignore if this is offtopic, but 2c from the back of my scratchy head-
> rs-232 is legally anywhere from +/- 3-25v either side of gnd,

https://en.wikipedia.org/wiki/RS-232#Voltage_levels

Close.  'Valid' is defined as +3 to +15 and -3 to -15V.  Max is +/- 25V
but is outside normal range.  I would hope to never see a range outside
of valid in normal operation.  The Max is just to handle unexpected
excursions.


> but I'd
> be careful sending more that ~12v to many consumer hardwares since
> who knows what corners they cut. in my experience most hardware uarts
> can deal with TTL level 0 | 5v (with hi/lo flipped vs real rs-232),

The UARTS can, but they are usually hooked to a TTL to RS-232 converter
and those vary all over the map on what they accept.

I would say about one half the serial hardware can deal with TTL levels
consistently.  The other half fail outright or get very flakey.

> but the addon serial adapters only support TTL sometimes, and GPSs
> often claim to output rs-232 but really output TTL. other times
> you'll need to whack something together with a max232 chip to do the
> translation from ttl to "true" rs-232.

Yup.  When in doubt be sure the levels are RS-232 or your serial port
can handle TTL.  This is doubly important wen passing PPS signals which
are shorter than the RS-232 spec defines.

RS-232-C specifies bit rates under 20Kbps!  That is a 25 micro Sec
pulse.  We often see PPS pulses only 1 micro Sec.  So put a scope on it
and be sure the signal is good.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588

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