External clock with Nucleo F446RE ..

[subu.rama]

I would like to experiment with feeding external clocks to the MCU on a Nucleo-F446RE (MB 1136 C) board.

I am not a hardware engineer, so pardon my ignorance with this. I am still learning!

From the schematics and physical board inspection of the Nucleo F446RE, X3 is unpopulated which is where the oscillator would go.

Ideally, I would like to *not* solder an oscillator on to the board but instead have a "clock/oscillator" on a separate board that I could use with this board or another STM/non-STM board.

Are such things available? If so, my next issue is how I would connect it PD0/PH0/PF0 and PD1/PH1/PF1 on the CN7 morpho connector. The schematic shows SB55 and SB54 for this but says, default: Open. What does "SB" mean here? Solder Bridge? What does that mean? I need to solder x to y? (I don't know what these x to y are)

Thank you

Subu

[subu.rama]

I don't know why the schematic excerpts didn't appear in my earlier post.

Here they are.

Subu

[Tesla DeLorean]

The NUCLEO provides an 8 MHz signal from the ST-LINK STM32F103 CPU, via it's MCO pin to the OSC_IN input of the STM32F446

Solder Bridge, yes there are small pads on the board, ST either places a zero-ohm (short/wire) resistor across them (connected), or leaves them open (disconnected), to facilitate different build functionality of the board.

If you disconnect the MCO signal be clearing the solder bridge that connects it, you can then supply a clock source from some where else, ie a OCXO or TCXO if that takes your fancy. You will also need to connect a common ground for such an external source/board.

[subu.rama]

Thank you, Clive. If I am understanding this correctly, you are referring to the MCO that's connected over SB50 to OSC_IN of the MCU. Yes, I understand that if I connect X3, I need to disable the MCO input by clearing SB50.

Do you know of any available boards that have an OCXO or TCXO that can be moved from board to board instead of being soldered on to a particular board?

I also understand that it's probably silly to connect a high precision oscillator to an eval board but my idea is to not tether it permanently to the Nucleo :-). Don't want to solder, desolder either.

Do I just get the component and put it on a proto board or some such thing? I understand the concepts but am lost in the mechanics!

Subu

[Tesla DeLorean]

Well you could jumper an external source to the header CN7, but you'd need to find someone with a soldering iron, and some skills to make SB55. Floating the solder between the two pads isn't hard, usually it takes skill not to do it.

You could perhaps socket or wire-wrap connectivity. You could make a small proto board to mount the oscillator, and connect power, ground and signals via jumper wires (schmartboard or dupont, etc)

I trained as an IC Design Engineer, I can solder and write software, as well as push polygons.

[subu.rama]

Sounds good. Thank you, Clive for the hints. I will learn about the schmartboard and dupont board usage etc.

Meanwhile, I will go ahead and solder it; will try it with a cheapo oscillator first to get practice 🙂

Subu

[Tesla DeLorean]

These things work a lot better than the push on dupont wire variants.

https://schmartboard.com/wire-jumpers/