What would be nice is something covering how to correctly calculate the loading caps for a MCU crystal. I don't think it's uncommon to think I have a 12pF xtal so I'll use 12pF capacitors, or tha app note shows 22pF caps so I need a 22pF xtal etc.
For a lot of MCUs it's close-ish and Just Works, though for radio MCUs (WiFi Bluetooth etc) it can make a difference.
One of the things I've noticed, if you're thinking of using an oscillator with a microcontroller, is that oscillators have pretty high current consumption, compared to modern microcontrollers. And it won't get shut off during the fancy low-power modes, either :-(
how one can measure these parameters on his own.
Quotehow one can measure these parameters on his own.Is determining the "correct" capacitance(s) for an external crystal feasible for an amateur with cheap equipment? Even if you carefully follow instructions, you usually hit a spot that reads "now make a wild guess at the stray capacitance of your chip packages and PCB."
I'm pretty certain that I've seen some datasheets that tell you to feed an external clock into X2
Quotehow one can measure these parameters on his own.Is determining the "correct" capacitance(s) for an external crystal feasible for an amateur with cheap equipment? Even if you carefully follow instructions, you usually hit a spot that reads "now make a wild guess at the stray capacitance of your chip packages and PCB."
Sure, I guess I could connect a frequency counter (or scope with freq counting ability) to some clocked pin and try "tuning" the crystals, but having a freq counter that is more accurate than the crystal is supposed to be seems ... somewhat unlikely.
I'm pretty certain that I've seen some datasheets that tell you to feed an external clock into X2
Some chips might tri-state the internal inverter output, otherwise that's not going to work unless X2 is the input.
I bodged on a through hole cap of approximately 20pF as a guess, in place of the missing 0402 SMD part, and it's worked perfectly since one would think the inductance of the long leads might be a problem but . These things seem forgiving until you need precision, I guess.
1. What would I do if X1 and X2 aren't the labels? I have a module with an mcu on it, it wants OSC-IN and OSC-OUT. I assume based on this guide that OSC-IN, I would connect to my clock's output, seems reasonable. And what about MCU OSC-OUT? Just leave it floating?
2. If I have the RTC / 32khz clock next to my main micro, and I want to get this output to my module that is 15mm away. Is there any serious concerns here? Impedance match? Keep on the top layer microstrip or move to a stripline even though its going to have two vias? There is a bluetooth radio on board so I am included to use a stripline.
3. Can I just tap off the OSC-OUT on my oscillator? I guess I could use a CLOCK-OUT signal from my micro to the module, but then I'm not sure I would have that in all power modes and conditions of my MCU. How would I go about figuring out what two micros need to be run off the same clock?
Probably not worth the 3 cents you would save.
Probably not worth the 3 cents you would save.
I don't get it?? You aren't suggesting that adding another time source for that module would be 3 cents right? It costs me more than 3 cents to pick and place any part. What is 3 cents?
Probably not worth the 3 cents you would save.
I don't get it?? You aren't suggesting that adding another time source for that module would be 3 cents right? It costs me more than 3 cents to pick and place any part. What is 3 cents?
3.5 cents: https://www.lcsc.com/product-detail/Crystals_huaxindianzi-DP2032K76812001_C17702403.html