SPI issue without V_BUS supplied

[deldipso]

I notified, the SPI doesn't seems to work if the USB is not plugged (or more directly V_BUS not supplied, it works if V_BUS only is supplied). So it is not working with a battery or an external power supply on VIN or VBAT if I make a simple project with just SPI. By not working I means the CLK and MOSI does toggle anymore in that situation. Just the CSB but it is controlled as a simple digital output pin. This is not an power supply issue. I even unplugged my SPI sensor, I see CLK and MOSI with USB but no anymore with external supply.

SPI CFG: SPI.begin(); SPI.setClockDivider(SPI_CLOCK_DIV64); SPI.setDataMode(SPI_MODE2); SPI.setBitOrder(LSBFIRST);

For an unknow reason, once I started to used the analogWrite() function, the SPI starts to work in any case, which is the workaround I currently use. It seems there is like a GPIO pin initialization issue when V_BUS is not supplied and the SPI only is used without analogWrite()...

[Antdigapony]

@deldipso I have checked this issue without the USB plugged in and I have found that the problem was with the GND pin. If there is only VIN connected to the 3V3 power supply - there is a problem, that you have mentioned. But if you connect the GND pin from the power supply too - all is OK(by the way it's a correct way of powering).

Maybe, in your case there is something else or whatever, but in my case SPI worked correctly without USB plugged in.