Thanks in advance for your help. I have the following circuit which is working fine. A 32 kHz oscillator NX3215SA (QUARZ SMD 32.768 kHz 3.2 x 1.5 mm) is simply connected to my MSP430F5438A on P7.0 and P7.1. The problem is when trying to get the 32 kHz oscillator frequency on TP64 in production we can not get the measure with the frequency counter (Keysight 53220A) while on oscilloscope (1M//16pF input) the signal and frequency are correctly visualized.

My questions are why can we get the signal on oscilloscope and not on frequency counter?

Trying to amplify the signal with an LM368 amplifier didn't help getting the measurement. Any idea on how we can get the measurement with the frequency counter?

enter image description herethanks

  • 1
    \$\begingroup\$ When configuring your frequency counter, did you set the input impedance to High-Z or 50-ohms? Was the input for the frequency counter also set to AC-coupled, with the 100 kHz high-pass filter disabled? (ref) \$\endgroup\$
    – nanofarad
    Commented Mar 4, 2022 at 16:52
  • 2
    \$\begingroup\$ Best way is to make the MCU output the frequency on another pin so the extremely sensitive high impedance crystal circuitry is not disturbed by measuring equipment. \$\endgroup\$
    – Justme
    Commented Mar 4, 2022 at 17:16
  • \$\begingroup\$ Tip: 'k' for 'kilo', 'K' for 'kelvin'. 'Hz' for 'hertz'. So, 'kHz' for 'kilohertz'. \$\endgroup\$
    – Transistor
    Commented Mar 4, 2022 at 17:24
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    \$\begingroup\$ Try using an oscilloscope 10:1 probe set to feed the Keysight 53220A \$\endgroup\$
    – Andy aka
    Commented Mar 4, 2022 at 17:40
  • 1
    \$\begingroup\$ P7.1/XOUT is high-impedance. Any capacitive loading of this point will shift frequency. I'd suggest a FET buffer (source-follower) circuit. It will still add some capacitance, but less than a 'scope probe. \$\endgroup\$
    – glen_geek
    Commented Mar 4, 2022 at 17:49

1 Answer 1


Measurements directly at a XTAL require a probe with low capacitance. It does work with the oscilloscope (1M//16pF input). So I would look up the frequency counter input specification, it should be comparable to the osc input. Select High-Z, AC-coupled and high pass filter disabled as suggested by nanofarad. If the input capacitance is higher than 16 pF you may try using a 10:1 osc probe if the input is sensitive enough for the 10:1 reduction.


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