[time-nuts] Of rubidium life and piggy-bank anemia....

[Bruce Griffiths]

Poul-Henning Kamp wrote:
> In message <475127AB.6010300 at xtra.co.nz>, Bruce Griffiths writes:
>
>   
>> You don't actually require a latch for each input as long as flag bits
>> (one per input channel) are used to denote which transitions occurred at
>> the latched count.
>> The flag bits should be latched along with the count.
>>     
>
> The latches are for resolving meta-stability issues between the two
> clock domains.
>
>   
You still dont need a dedicated time count latch for each channel.
A pair of time count latches should suffice (one for each
counter/synchroniser clock transition polarity) plus a flag bit for each
channel.
Latch the flag bits and the count in both sets of latches.
>> Using a PCI card is perhaps a recipe for planned obsolescence.
>> If the input transition rates are relatively low (eg with PPS inputs)
>> then an onboard microprocessor with a serial port has more than
>> sufficient bandwidth to keep up.
>>     
>
> Yes, but using a PCI card makes it possible to use the setup as
> timebase for your computer as well :-)
>
>   
It can also add considerable ground noise potentially corrupting
otherwise clean signals.

Bruce