GPIO pins output with 1.8V supply

[Dan Colob]

I am connecting 1.8V supply to VDDH and VDD so none of the REG will be on. Will I get 1.8V out on the GPIO? I am trying to connect LED on the pins but with 1.8V out that will be hard, is there a way to tune this and reduce the current coming out?

[ketiljo]

The GPIO voltage is always referred to VDD on nRF devices. No LED is going to work well with only 1.8 V. A red LED needs 1.9 V, so you need a higher power supply. In any case, the GPIO can't deliver more than 5-10 mA so in most cases, you can connect the LED directly to the GPIO with no series resistor. You need more than 1.8 V though.