NRF52840 GPIO output voltage at 1.8V when 3.3V is supplied?

Question

Hello all, 
 I am currently using an MDBT50Q-DB-40 from Raytac with the NRF52 DK (PCA10056) with nrf connect in vs code. 
 Very simply, I'm setting a GPIO to go high and low. 
 The voltage I'm getting from the GPIO is not what I expected. I'm seeing ~1.8V instead of 3.3V. 
 Is this expected behavior? The Raytac board is definitely supplying 3.3V to VDD. 
 Do I need to configure a register somewhere, and if so how should I do that? 
 Thanks for all the help, 
 Joe

Kenneth · Answer

Hello, 
 I assume you are powering the module to VDDH (not VDD): https://docs.nordicsemi.com/bundle/ps_nrf52840/page/power.html#ariaid-title3 https://docs.nordicsemi.com/bundle/ps_nrf52840/page/power.html#ariaid-title5 
 In which case you need to set the voltage on the pins through the UICR register (though make sure VDDH is 0.3V higher than what you want to output to VDD): https://docs.nordicsemi.com/bundle/ps_nrf52840/page/uicr.html#register.REGOUT0 
 Several ways UICR can be set, you can for instance take a look at how it's done \zephyr\boards
ordic
rf52840dongle\board.c 
 Though if you want 3.3V you likely should change from UICR_REGOUT0_VOUT_3V0 to UICR_REGOUT0_VOUT_3V3 in the above file. 
 All that said, based on your description you might have powered the module wrong, if you already have 3.3V, then you need to supply 3.3V to both VDD and VDDH. 
 Hope that helps, Kenneth

NRF52840 GPIO output voltage at 1.8V when 3.3V is supplied?

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