[time-nuts] gpsd 1pps pulse?
albertson.chris at gmail.com
Mon May 6 12:04:16 EDT 2013
The computer only looks at the leading edge so the pulse width does
not matter as long as the cable is short. look at what kind of signal
is required by the serial port on the PC. Many of them will accept a
TTL level 5 volt signal but you may have to level sift it to RS-232
levels (plus and minus about 9 volts) If you are driving a long
cable you may have to buffer it.
Whatever you do make sure the polarity is correct. RS232 data signals
use "negative logic" with 0 meaning 1 but rs232 control signls use the
other convention. If you get the polarity wrong the timing is "off"
by the width of the pulse. So you get a 10 uS bias. Having the PPS
inverted is a common error.
On Mon, May 6, 2013 at 6:38 AM, Chuck Forsberg WA7KGX N2469R
<caf at omen.com> wrote:
> I would like to set up a NTP server on a machine running Linux
> (currently Korora 18).
> What are the requirements for the 1 PPS signal fed to the carrier detect
> I presume the 10 us 1pps from the Thunderbolt is too narrow.
> I assume the rising edge of CD is the one gpsd triggers on.
> Chuck Forsberg WA7KGX caf at omen.com www.omen.com
> Developer of Industrial ZMODEM(Tm) for Embedded Applications
> Omen Technology Inc "The High Reliability Software"
> 10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430
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