It is likely that the radio data service patent holders require this. 
If the chip simply demodulates the digital signal and presents the
data as-is, then one must be privy to the protocol.

-Adam

On 5/1/06, Rick Hochhalter <rhochhalte@cableone.net> wrote:
> On Mon, 01 May 2006 23:21:41 +0100
> Philip Pemberton <philpem@dsl.pipex.com> graced us with this prophetic message:
>
> > Only thing I'm worried about is the lack of a datasheet,
>
> This is what gets me.  Why is the datasheet only available under an NDA?  Do they
> NOT want people to design their stuff into projects, i.e. they actually don't want to sell
> their stuff to others?  This is totally stupid, and it's not just with this chip but with (at
> least some) of their other chips, too.
>
> Rick
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