Digi International’s SX RF modems use 1-Watt industrial-grade 900 MHz long range SX radio technology for wireless cable replacement applications. They are flexible, easy to use and utilize DigiMesh® wireless networking protocol, with redundant mesh network operation and support for low-power sleeping nodes. Available interfaces to the modems include RS-232, RS-485, USB, Analog I/O and Digital I/O.
more info at eeWiki link https://www.eewiki.net/display/Wireless/Xbee+SX+RS232+RS485+RF+Modems
Resources
RS232/RS485 SX Xbee modem ; Digi-Key part# 602-1980-ND ;
https://www.digikey.jp/product-detail/ja/digi/XM-X9-3P-U/602-1980-ND/6619081
XBee SX RF Modems User Guide XBee RF Modems User Guide
If you have any questions, feel free to post them under this thread.