Russound CAA66 serial strangeness

["Max Metral" <memetral@xxxxxxxxxxx>]

So I just got a Russound CAA66 multizone controller.  Looks interesting.
The serial protocol is public, so I'm writing some code to interface my
existing system with it.  The docs say "19200 baud with 1 start bit, 1 stop
bit, no parity, no flow control."  I think this means "19200-8-N-1".  The
strange thing is, it seems to "see" my messages fine.  But it's acks are
supposed to start with 0xF0 and end with 0xF7.  Instead, they start and end
with 0x3F.  Does this make any darn sense?  The rest of the characters
actually seem fine, just the start and end don't match.  I suppose the most
likely candidate is bad docs, because I don't see a transformation that
makes both 0xF0 and 0xF7 into 0x3F and then suddenly resolves itself on the
next byte.

--Max