Radio control binding

[Mike O'Dell]

thanks for the pointer on the DSMX wire protocol

the air interface is described by the data sheet
on the radio section of the part mentioned.
the air interface uses both CDMA and frequency agility.
49 Gold codes are provided in hardware (so you don't have 
to screw them up programming them) and 79 1-MHz channels
in the RF section. Unlike all WiFi chips which are all
zero-IF designs and hence have essentialy *no* RF selectivity
as fars as the wifi "channels" are concerned, this radio is
uses a Low-IF with matched filters so the agility of the
synthesizers is not wasted. It can do this because the 
data rate is a tiny fraction of wifi, but it's not bad
if one is frugal with the bits it delivers. The chip has
3 modes which trade chip-rate for data rate. The lowest
bit rate but highest chip rate (and hence highest coding gain)
uses 64 chips per bit which provides a data rate 16Kbits/sec.
Not blistering performance but high coding gain for noisy channels.
next is 32-chips/bit which gives 32Kbits/sec. Then there is
a double-data-rate mode which uses 32-chips/bit but sends two
data streams for a 64Kbits/sec data rate.

the chip Mark cited is an 8-bit MCU with the radio all on 
one chip. The radio is DSP-based and generates GFSK directly
with a vector modulator algorithm for TX. the RX side uses
a high-quality FM demod to recover the data.  All in all
i looks like a very nice part.

"binding" is clearly the "transmitter" and "receiver" coming
to agreement on which RF channel looks best and then which
of the Gold codes to use. Both ends can transmit so it really
is a conversation.

   -mo