Hi If you go back into the archives, there are a long series of posts about the tuning word and tuning behavior of the 5880. Simple answers: No the real resolution is not the same as the LSB on the tuning word. The tuning is closer to 1x10^12 than to 1x10^-15.
Bob > On May 7, 2016, at 12:51 AM, Nick Sayer via time-nuts <[email protected]> > wrote: > > I got a second 5680 in the mail the other day and so far my firmware isn’t > bricking it, so.. yay. > > A couple of odd things have turned up, though. > > 1. So far as I can experimentally tell, the tuning step on this unit is 50 > times larger than the 17E-15 quoted by FEI. Either the tuning curve is not > linear or the tuning range is not what they claim (or both). I’d like to get > a feel for whether the standard deviation of the mid-range (near zero) tuning > step is. Is it closer to what I’m observing or FEI’s spec? The answer will > instruct me on how to pick the PLL gain constant for the firmware. > > 2. Directly clocking an AVR from the 5680A is unreliable prior to lock. I > haven’t exhaustively examined the startup behavior of the 5680, but power-up > reset of my GPS board used to not happen a lot of the time, and manual reset > was required. The AVR datasheet says that as long as the clock frequency is > kept within 2% from cycle to cycle that that’s ok, but either this 5680A > isn’t doing that or the AVR datasheet is wrong. Fortunately, there’s a > software workaround: fuse the controller for the internal 8 MHz oscillator > and switch over (I was surprised to learn that changing system clock sources > on the fly is an option) to the 5680 only once a physics lock is indicated by > the lock pin. That seems to be acceptably reliable. My purpose in mentioning > it is to see if anyone has examined the pre-lock behavior of the 5680 (I > understand it’s not a particularly interesting question) to see exactly how > jumpy it really is before it locks. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
