I just need some clarification of my circuit

Oscillator: So for my circuit I want to be able to program it via USB, the datasheet gets a bit confusing to me tho. If I read the datasheet correctly I need an 18.432MHz clock with 10pF capacitors tied to ground for USB application, does this sound right?

GPIO: Other than PA0, 1, 2 GPIO can only drive 8mA signals will this be enough to drive a gate on a ULN2003? I couldn't find a base current requirement. I'll be sinking a 3v relay on the other side of the gate.

Reset (kinda also GPIO): If all GPIO is pulled high until initialization is complete could I leave pins PA0, 1, 2 floating and still drive the TST pin high on boot to perform the SAM-BA Recovery Process?

  • \$\begingroup\$ Link to the data sheet and the gate you mention and how its connected to the ULN2003. You might want to link the 2003 too. \$\endgroup\$ – Andy aka Jan 16 at 15:32
  • \$\begingroup\$ @Andy aka I was inferring the transistor base of the 2003 as a "gate" \$\endgroup\$ – Nathan Johnson Jan 16 at 15:37
  • \$\begingroup\$ In regards to the oscillator, you are correct that you'll need a 18.432 MHz source for USB operations. That's just the way that Atmel designed the part. In regards to the capacitors, these are required to provide the proper load on a crystal, if that's what you intend to use. You'll need to match the load capacitance to the specific crystal that you'll use. You can go to the crystal manufacturer's datasheet to find information on the it's load capacitance. Atmel has already provided internal capacitance to this part, nominally 20pF, so the external parts are used to make up the difference. \$\endgroup\$ – BEE Jan 16 at 18:11

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