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Chapter 8: GPS and a Real- T ime Situational Displa y 207

center of the board. There is a microSD socket situated between the XBee sockets. The BOE
designers also included eight socket pins where key XBee pins are easily available for
interconnections. These pins are part of a 10 × 2 socket located above the right XBee socket.
I will next examine the XBee hardware to show how this clever design makes wireless
transmission so easy.

XBee hardware

All the electronics in the XBee hardware, except for the antenna, are contained in a slim
metal case located on the bottom side of the module, as may be seen in Figure 8.17. If you
look closely at the figure, you should see the bottom of the antenna wire, which is located
near the top left corner of the case. While Digi International is not too forthcoming regarding
what makes up the electronic contents of the case, I did determine that the earlier versions
of the Series 1 XBee transceivers used the Freescale™ model MC13192 RF transceiver. This
chip is a hybrid type, meaning that it is made up of both analog and digital components. The
analog components make up the RF transmit-and-receive circuits while the digital
components implement all the other chip functions. It is a complex chip, which is the reason
why the XBee module is so versatile and able to automatically perform a remarkable number
of networking functions. Table 8.5 shows a select number of features and specifications for
the MC13192.
The XBee module implements a full network protocol suite (which is discussed below in
the software section), but from a hardware perspective, it means that there must also be a
microprocessor present in the electronics case. From my research, I cannot determine which
type of microprocessor it is, but I am willing to make an educated guess that it would be a
Freescale chip, based upon the reasonable assumption that the MC13192 would be designed
™
to be highly compatible with the company’s own line of microprocessors. One other factor
supporting my guess is that Digi International has recently introduced a line of programmable
XBee modules named XBee Pro SB that use the 8-bit Freescale S08 microprocessor. Of
™
course, being able to put your own programs into the XBee would eliminate the need for the
Mini, but that would not be as much fun and would probably be a bit limiting, given the
tremendous capabilities of the Propeller chip.

Figure 8.17 XBee electronics case.