[time-nuts] NTP/1-PPS/RS232 question

[Chris Albertson]

You only need ONE inverter gate.

The purpose is the flip the pulse.  The MAX 232 chip flips the logic
once which works fine for the data but you need to flip the control
lines (maybe if the GPS reciever did not already do this for you.)

Flipping the PPS has the effect of moving the pulse by the length of
the pulse so one gate in this case will move the pulse by 100MS.

On Sat, Sep 7, 2013 at 9:22 PM, Bob Bownes <bownes at gmail.com> wrote:
> 100ms is an awful lot of 'inverter gates'!
>
> On Sep 7, 2013, at 23:15, Chris Albertson <albertson.chris at gmail.com> wrote:
>
>> With RS232 the data uses negative logic (low is "1") and the control
>> lines use positive logic (high is "1".)   That is, a control line is
>> "asserted" when it is at logic 0, a positive voltage.
>>
>> Some one at one time must have thought this made sense.
>>
>> The good news is that a mistake is easy to detect and fix.  If the
>> pulse is 100MS long and you have it inverted then your time will be
>> off by 100MS.   When you are designing the board put in some extra
>> inverter gates
>>
>> On Sat, Sep 7, 2013 at 7:15 PM, Mark Sims <holrum at hotmail.com> wrote:
>>> I got in those Adafruit GPS boards.  They are a very nice little GPS.   VERY sensitive.  I could get good lock indoors on my (windowless) kitchen floor.  The house is 2 story,  stucco with wire mesh in the stucco.   I could also get lock in a restaurant that had a tin roof.  We were far from any windows.
>>> The 1PPS signal is normally low and pulses high for 100 milliseconds.  The RS-232 adapter board that I built feeds this into an RS-232 transmitter chip (MAX3232),  so on the interface connector CD will be at +V and pulse down to -V.  Is this what stock NTP likes?
>>> Also,  I laid out the adapter board so it an accommodate a Trimble Resolution T or a Crius CN06 receiver.  The Crius receiver uses a U-Blox NEO-6M receiver.  They can be had for around $22 at HobbyKing.   They seem to perform even better than the AdaFruit module.  It looks like you will need to bodge a wire onto the TIMEPULSE pin to use it for 1PPS.
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>>
>>
>> --
>>
>> Chris Albertson
>> Redondo Beach, California
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-- 

Chris Albertson
Redondo Beach, California