See the document here.
I am interested on using external interrupts, and trying to configure NVIC at register level. The statement below, which can be found in page 215, confused me:
Each priority field holds a priority value, 0-255. The lower the value, the greater the priority of the corresponding interrupt. The processor implements only bits[7:4] of each field, bits[3:0] read as zero and ignore writes.
Especially the bold part.
If that explanation was not present, I would directly think that I can write any number (0-255) to those 8 bit fields to set the priority. But now, I am confused such that whether I can use bits [3:0] or not.