Why my result converted by saadc can't be consistent with voltage from the pin?

[Jack-h]

It's my question. I use saadc single mode from nrf52832 to sample voltage .When the original voltage is 24 V ,measurement of the pin is 2.8v,I set the resolution to 10 BITS,I think result should be 2.8/3.3*1024(868), but why my result is 808 all the time? Who could help me soon?

[Jack-h]

input range is assurely 3.3 v.It's the fact that I misunderstand the meaning of 2.8/3.6*1024--I always use 3.3 to replace 3.6.

[Carsten Wulff]

The reason I'm asking is because the SAADC cannot be configured with 3.3V full-scale range and internal reference. Are you using VDD as reference?