This is more a question for s.e.b. (x-posted there)
Looking at the datasheet
formatting link
then you have: Assuming the 16 pin DIP/SOP style package Low levels on
Input '5' (pin 2) Input ''8' (pin 5) Input ''2' (pin 12)
This is a priority encoder with active low inputs. Therefore, the highest 'value' input, when active, is the encoded value at the output. In this case, that is input ''8'
(See the truth/function table on page 2 of the datasheet)
So the output will be: A = H B = H C = H D = L
(Active low outputs, encoded hex '8', 0111 - invert for active high for clarity = 1000)
Cheers
PeteS