Simplified View of the Actual XBee Hardware

Figure above is a simplified depiction of the XBee module’s internals. Incoming data flowing through the DIN pin is buffered by the DIN buffer until it can be transmitted. As programmer and commander, you have the option of sending characters as they enter the DIN pin or buffering up a number of characters to send as a packet. When the XBee module isn’t sending characters, it can rest in Idle mode, enter Receive mode, process a command, or just sleep it off. The bulk of the subsystem boxes shown in Figure above are contained within two Freescale Semiconductor physical ICs: an MC9S08GT60 microcontroller and an MC13193 802.15.4 RF transceiver IC.