I have a custom PCB with a 32u4 running fine with an 8MHz external oscillator. I burned the bootloader and loaded my sketch with an UNO using Arduino as ISP.
I have no USB on my PCB nor do I need precise timing, so I wanted to see if I could simplify things by removing the external oscillator and caps.
Reading the 32u4 datasheet it states "The device is shipped with Low Power Crystal Oscillator (8.0 - 16MHz) enabled and with the fuse CKDIV8 programmed".
With that, can I simply hook my PCB (assuming a factory fresh 32u4) via ISP to the UNO as before and in IDE just use Sketch > Upload Using Programmer? Basically not burning any bootloader at all.
Also, in IDE I have been choosing the Sparkfun ProMicro 3.3v, 8MHz board. Can I still use that selection?