[LinuxPPS] Trying to get parallel port client working on 2.6.26

[Hal V. Engel]

On Friday 19 September 2008 02:17:42 pm clemens at dwf.com wrote:
> OK, this is something that I knew once, but forgot when I was trying to
> test the parallel port myself.
>
> On the SERIAL port, the PPS signal is active POSITIVE.

This is definitely correct if you are using the assert event but you can also 
use an inverted signal (IE. a PPS pulse that goes from zero to -5V) but you 
have to use the clear event and not the assert event.  Remco has his OnCOre 
UT+ hocked up this way because he has an inverter between the GPS and the DCD 
pin. 

See http://rembl.org/index.php/2008/04/19/motorola-oncore-ut-and-linuxpps/

>
> On the PARALLEL port the PPS signal is active NEGATIVE.
>
> (I sure hope I havent got that reversed).
> In any case, a signal that will work on one wont work on the other.
> Be sure with your scope/digitalVM/LED that the sign of the pulse is
> correct.