[ntp:questions] Re: Looking for time sync hardware supported under Linux for under $400?

Hal Murray hmurray at suespammers.org
Tue Jan 17 21:10:57 UTC 2006

>The documentation for it says that the serial interface is TTL levels
>(which are 0-5v, if I understand correctly), rather than what would be
>expected by a PC serial port (which are 0-15v, again IIUC).

The transmit side of RS-232 is supposed to go below 0.  I'd
have to find the specs to get the details.

Common chips using flying cap switching work off 3V so they
can only make +6V and -6V.

>Can this just be connected to the PC serial port, or will I have
>to build/buy a TTL -> RS-232 converter/adapter?

Just plug it in.  It will most likely work.

All the RS-232 receivers I've ever worked with actually switch at
around 1.4V, the old TTL threshold.  If anybody tried to sell a chip
that did anything else they would break all sorts of kludgy gear.

>I looked through the 'Comprehensive list of clock drivers' supplied with
>the NTP software, and didn't see this device mentioned. Is it know by
>another name to the NTP software?

Use the NMEA driver.

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