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I was using such an extension shield:

enter image description here

It is built using an MCP2515 (datasheet) controller and a TJA1040 transceiver.

The resonator on it has undefined signs, so I wanted to use a logic analyzer (DSLogic plus) to check its frequency (maybe it wasn't a good idea from the very start).

So I connected it to the OSC1 input of MC (only later I realized, that I could have used the crystal output soldered on the bottom of the board, and maybe nothing wrong would have happened).

enter image description here

But it seems I suddenly soldered the OSC1 and Vss (ground) pins on MC together, so now it is not working, and I wonder if it is just the crystal, and if I can exchange it, or if it is MC and nothing would help.

P.S. here is a comparison of Arduino Uno and that shield's clock frequencies after the last one being broken.

enter image description here

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  • \$\begingroup\$ On that low resolution picture one can make out 8.000M, which would strongly suggest 8 MHz. \$\endgroup\$
    – Arsenal
    Feb 23, 2022 at 9:51
  • \$\begingroup\$ this photo was not taken by me, it is from the internet. My one contains D0695342C sign. \$\endgroup\$
    – lazba
    Feb 23, 2022 at 9:57

3 Answers 3

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Shorting the OSC1 input to ground will not damage the circuit.

Also crystal circuits are extremely sensitive and they are not logic level signals, so trying to measure OSC1 pin with a generic USB logic analyzer is useless, it will most likely just disturb the oscillator circuitry too much and it stops oscillating, and even if it did continue oscillating, the amplitude and DC bias may not be compatible with logic analyzer input levels.

The CAN controller also starts up in configuration mode so the oscillator may be turned off, and so it will need to be turned on at chip init.

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The oscillator circuit is an amplifier with feedback, and with the crystal placed in the feedback path so that the oscillator will favor that frequency.

Note that OSC1 is the input to the amplifier. It is high impedance and very sensitive to being probed. Connecting equipment to this lead may cause it to stop oscillating altogether. Also shorting it to ground will definitely stop it from oscillating, but it won't hurt the crystal or the chip. You do need to remove the short for it start working again.

OSC2 is the output of the amplifier, much lower impedance, and that is where you should attach your equipment. You'll get better results there.

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    \$\begingroup\$ The chip has a separate output pin for oscillator signal so it would be even better place to connect equipment. \$\endgroup\$
    – Justme
    Feb 24, 2022 at 8:42
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The oscillator frequency can be found on the crystal. It's 8MHz. Random site working with this module with pinout and explanations

You can't plug an USB analyzer on that type of signals, it's too low to be seen by any sort of logic level analyzers.

For your problem replace the can board, you could have damaged something other than the crystal by doing your experiment.

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  • \$\begingroup\$ I can regulate treshold level from 0 to 5V and also I measured arduino frequency and it is ok. Maybe problem with this sircuit was in it being much more sensitive for external loads, so maybe I had to put some high resistance to it in parralel but not rely only on LA internal one. BTW it is working now, so maybe it had to have some time for rest, xD. \$\endgroup\$
    – lazba
    Feb 23, 2022 at 9:49
  • \$\begingroup\$ Also I wasn't able to find frequency on the crystal as it doesn't contain that sort of information (I suppose that it is its part number, but I haven't found it in google). Though changing prescaler I found that it is really 8MHz, so you are right. \$\endgroup\$
    – lazba
    Feb 23, 2022 at 9:49
  • \$\begingroup\$ I hadn't mentioned it eralier, but this board has different modifications with 8,16 and 20 MHz oscillator. \$\endgroup\$
    – lazba
    Feb 23, 2022 at 10:00

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