What radio are you using? Only XBees that run the Zigbee protocol need a coordinator. If you are using an XBee Zigbee then the S2 and S2B need to be flashed to different firmware depending on the function set. For the S2C you set the CE parameter to set it to be a coordinator and set sleep mode if you want it to be an end point. On S2C leaving both CE and SM at zero makes it a router.