First, I apologize if this ends up being posted twice. 14 hours without it even showing up on the news server I originally posted from gives me reason to believe that someone along that path found my wisdom so profound that they diverted it off the wire for their selfish benefit. ;-)
Now as to the OP's query, but from a different news server:
Because then all PIO bits would be affected, which is fine if the caller already knows how the PIO is currently set, but using a mask allows the caller to specify *which* bits to 'merge' in with the PIO setting and which bits to ignore.
"mask" and "bits" allows you to set and clear bits with a single function (and a single call to that function). "mask" determines the affected bits and "bits" sets or clears only those bits.
With Pioset ( uint16 bits ) you would need a separate Pioclr ( uint16 bits ) function.
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