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

[Bob Bownes]

Exactly. And, as someone else pointed out, you then need to delay it 900 ms to put it back in the right place, which would take a lot of gate delay. This is time nuts after all...

On Sep 8, 2013, at 11:08, Chris Albertson <albertson.chris at gmail.com> wrote:

> 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
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