Original SRV-1 radio board had direct support for XBee. See
http://www.surveyor.com/blackfin/#blackfin1 Legacy Boards
* Matchport/XBee Radio Module EAGLE Files: bfin-radio-v2.sch bfin-radio-v2.brd
Note that XBee interfaces at 115kbps and needs hardware flow control, so actual throughput is 80kbps. I think also, you might have to program the Blackfin UART for 112kbps instead of 115kbps, since there was a clock mismatch that caused problems when we tested this a few years ago.