78 MAKING THINGS TALK mode with ATUCL\r and following the same steps as previously. Because the AT commands are just text strings, you can easily use them in microcontroller programs to control the module, make and break connections, and exchange data. Because all the commands are in ASCII, it's a good idea to exchange data in ASCII mode, too. So the data string that you set up earlier to send Monski's sensor readings in ASCII would work well over this modem. X Conclusion The projects in this chapter have covered a number of ideas that are central to all networked data communication. First, keep in mind that data communication is based on a layered series of agreements, starting with the physical layer, then the electrical, the logical, the data, and finally the application layer. Keep these layers in mind as you design and troubleshoot your projects and you'll find it easier to isolate problems