[time-nuts] Trimble Thunderbolt 1pps

[Chris Albertson]

Specs or not.  In real life most computers will accept a TTL level
serial signal.  They will also accept one with RS232 levels.
The thing to keep straight is the RS232 uses negative logic for data,
positive logic for control lines and TTL is always positive logic.
You may need some inverters.

So what to send?  If the cable is 2 or 3 feet tit hardy matters.  If
the distance is "moderate" buy a Max232 chip and if the distance is
"far" don't use RS232.  "moderate might go up to about 100 feet if you
use quality cable. and don't route it in the ceiling over florescent
lights and AC power lines.

My solution was to buy a few of these DB9 connectors that have the
MAX232 chip builtin.  They cost about the same as normal connecters,
find them on eBay.

On Mon, Jan 27, 2014 at 6:08 AM, Attila Kinali <attila at kinali.ch> wrote:
> On Sun, 05 Jan 2014 13:35:43 -0800
> Hal Murray <hmurray at megapathdsl.net> wrote:
>
>>
>> attila at kinali.ch said:
>> > Also keep in mind that RS-232 relies on the voltage going negative to encode
>> > a "1". I.e. getting 0V is not enough and might only work by chance with some
>> > RS-232 receivers.
>>
>> I think there are 2 parts to this discussion.  What do the specs say, and
>> what actually happens in the real world?
>>
>> I think the specs say that -3 to +3 is no mans land.  A valid signal must be
>> over +3 or under -3.
>
> IIRC that's right. But i haven't had a look at the standard for a very long time.
>
>
>> In practice, the receiver chip only has one power supply.  It would take
>> extra work to make the switching threshold below ground.
>
> That's not correct. Standard transceiver chips (like the MAX232 family)
> have an integrated charge pump to get a negative power supply.
>
> I have never done exact measurements, but my experience is that going
> a bit (0.5V?) below GND and slightly more above GND is enough to get
> a proper 1/0 detection. Of course, if you rely on that you get a very
> poor noise performance.
>
>
>
>                         Attila Kinali
>
> --
> The trouble with you, Shev, is you don't say anything until you've saved
> up a whole truckload of damned heavy brick arguments and then you dump
> them all out and never look at the bleeding body mangled beneath the heap
>                 -- Tirin, The Dispossessed, U. Le Guin
> _______________________________________________
> 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