From Jeff's Frequency Standard, we injected a 10MHz signal into the Propeller at the XIN pin via a DC blocking capacitor, and set the Prop clock configuration to:
CON _CLKMODE = XTAL1 + PLL8X _XINFREQ = 10_000_000
Note: 10MHz is above the suggested 4 to 8MHz for clock input, but TCXO's do not seem to be available for those frequencies. We were just experimenting with 10MHz.
It worked, The results looked very-very good. Jeff displayed the receive signal without Jitter or Frequency Drift.
The Prop PLL circuit runs at 16 times the injected frequency, or 160MHz, and then the PLL8X config provides the standard 80MHz for the rest of Prop.
Jeff's Freq Standard contains an inexpensive and readily available 20MHz TCXO. His Freq Standard provides a switch to divide by 2, which was used for our tests.
The 20MHz TCXO used for this test is available from Mouser, a similar 10MHz part CVT32-10.000 is also available for $8.00.
We plan to use the following circuit.
Propeller - TCXO Circuit