robindegen wrote:
When I measure the XTLO pin with my scope, I see a nice 1.84mhz oscillator signal. When I measure XTLI i see 2.5ish volts but no oscillation. Is this correct? Considering the naming of the pins, I expected to see a signal on XTLI instead (as in I for Input?)?
I've also tried putting the 27pF cap on pin 7 instead, and I even tried removing it completely. Both didn't change anything.
robindegen wrote:
Also for reference in case anybody is wondering: It's normal to see the oscillation only happen on pin 7. The WDC just uses confusing naming of pins if you ask me.
Think of pin XTLI as an input to a sensitive amplifier, and XTLO as the output from this amplifier. When you put your 'scope probe on XTLI, the capacitance and resistance of the probe, lead and input of the 'scope are enough to degrade the signal. The input to the amplifier is then outside the correct range, so the circuit stops oscillating.
Whereas, when you test on XTLO, there is still enough drive so the circuit continues to oscillate.
Nearly all crystal oscillator circuits need either one, or sometimes two loading capacitors to help the crystal to oscillate in the correct manner.
Mark