On 09/30/2020 01:32 PM, Clark (US), Kenneth C via USRP-users wrote:
Hello,
The B210 has separate connectors for a 1-PPS and 10-MHz reference.
But the B205 has only the one SMA connector, which is indicated to be dual
purpose (1-PPS or 10-MHz).
Is it possible connect both, using a GPIO pin for the 1-PPS?
If so, which pin? How to enable?
Thanks,
Ken Clark
The B205 external clock apparatus is quite different than on other
USRPs. Rather than having an analog clock PLL chip, there's
a DPLL implemented in the FPGA.
That DPLL automatically "figures out" whether you have 1PPS or 10MHz
coming into the external clock input--of which there is only one.
Once it figures that out, it automatically steers the internal VCTCXO
based on the estimates of the internal-to-FPGA DPLL.
My recollection is that you set PPS to "internal", and REFCLOCK to
"external", and it will act appropriately.
You *could* re-jig the FPGA code to have both a 10Mhz reference, and a
1PPS coming in on a GPIO--but that isn't built in.
Ken Clark
Email: kenneth.c.cla...@boeing.com
Mobile: +1 561 398 1050
DRT, Inc.
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