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

David J Taylor david-taylor at blueyonder.co.uk
Mon Aug 19 04:29:54 EDT 2013

From: Hal Murray

> Yes, this is right.  But watch the polarity.  It is easy to get it wrong.
>  In RS-232 the controls pins are different from the data pins.

The reference implementation of ntpd can accept either polarity.

It's one of the fudge options.

Although, IIRC from discussions with Dave Hart, the Windows port can only 
accept the normal positive-going signal on the DCD line.  The devices I've 
tested all have positive going signals.  Pulse width is typically 100 or 200 
milliseconds, with a few receivers giving a much shorter pulse.

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Email: david-taylor at blueyonder.co.uk 

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