Making Things Talk

222 MAKING THINGS TALK

Look, Ma: No Microcontroller!

Since the beginning of the book, you’ve been working with programmable micro-

controllers, writing the whole program yourself. You don’t always have to do this. The

various network devices you’ve been working with — the Lantronix devices, and XBee

and Bluetooth Radios — all have their own microcontrollers built in. Some of them have

their own digital and analog input and output pins. You can configure these devices to

activate and respond to these I/O pins with network messages, but you need to learn

their protocols first. To give you some examples of how you can use these network

modules to their full potential, none of the projects in this chapter use programmable

microcontrollers.

Sessions versus Messages

In Chapter 5, you learned about the Transmission Control

Protocol, TCP, which is used for much of the communica-

tion on the Internet. To use TCP, your device has to request

a connection to another device. The other device opens

a network port, and the connection is established. Once

the connection is made, information is exchanged, then

the connection is closed. The whole request-connect-

converse-disconnect sequence constitutes a session. If

you want to talk to multiple devices, you have to open and

maintain multiple sessions. Sessions characterize TCP

communications.

Sometimes you want to make a network in which objects

can ...