Making Things Talk

246 MAKING THINGS TALK

Directed Messages

The more common way to use sessionless protocols is to send directed messages to

the object to which you want to speak. You saw this in action already in Chapter 6, when

you programmed your microcontrollers to speak to each other using the XBee radios.

Each radio had a source address (which you read and set using the ATMY command)

and a destination address (which you read and set using the ATDL command). One

radio’s destination was another’s source, and vice versa. Though there were only two

radios in that example, you could have included many more radios, and decided which

one to address by changing the destination address on the fly.

Sending UDP Datagrams To

and From a Lantronix Device

So far, you’ve used the Lantronix devices to communicate

via TCP, but they can also send and receive UDP packets.

To do this, you have to set the connectMode appropriately

(see “Configuring the Micro” in Chapter 4 for configuration

instructions) and set an address to which the datagrams

will be sent. You can also control when datagrams are sent;

for example, the default is 12 milliseconds after a serial

byte is received, but you can change the time delay, or you

can set the device to send after it receives a specific string

of characters.

To send directed UDP packets, you have to set the connect

Mode to 0xCC, which sets your device to accept any

incoming UDP ...