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Events and Callbacks

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Event Types and Callback Properties Responding To Event Information Example: Using Events and Callbacks

Event Types and Callback Properties

The event types and associated callback properties supported by TCP/IP and UDP objects are listed below.

TCP/IP and UDP Event Types and Callback Properties

Event Type	Associated Properties
Bytes available	BytesAvailableFcn
	BytesAvailableFcnCount
	BytesAvailableFcnMode
Datagram received	DatagramReceivedFcn (UDP objects only)
Error	ErrorFcn
Output empty	OutputEmptyFcn
Timer	TimerFcn
	TimerPeriod

The datagram-received event is described below. For a description of the other event types, refer to Event Types and Callback Properties.

Datagram-Received Event

A datagram-received event is generated immediately after a complete datagram is received in the input buffer.

This event executes the callback function specified for the DatagramReceivedFcn property. It can be generated for both synchronous and asynchronous read operations.

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Responding To Event Information

You can respond to event information in a callback function or in a record file. Event information stored in a callback function uses two fields: Type and Data. The Type field contains the event type, while the Data field contains event-specific information. As described in Creating and Executing Callback Functions, these two fields are associated with a structure that you define in the callback function header. Refer to Debugging: Recording Information to Disk to learn about storing event information in a record file.

The event types and the values for the Type and Data fields are given below.

TCP/IP and UDP Event Information

Event Type	Field	Field Value
Bytes available	Type	BytesAvailable
	Data.AbsTime	day-month-year hour:minute:second
Datagram received	Type	DatagramReceived
	Data.AbsTime	day-month-year hour:minute:second
	Data.DatagramAddress	IP address string
	Data.DatagramLength	Number of bytes received as double
	Data.DatagramPort	Port number of sender as double
Error	Type	Error
	Data.AbsTime	day-month-year hour:minute:second
	Data.Message	An error string
Output empty	Type	OutputEmpty
	Data.AbsTime	day-month-year hour:minute:second
Timer	Type	Timer
	Data.AbsTime	day-month-year hour:minute:second

The Data field values are described below.

AbsTime Field

AbsTime is defined for all events, and indicates the absolute time the event occurred. The absolute time is returned using the MATLAB Command window clock format.

day-month-year hour:minute:second

DatagramAddress Field

DatagramAddress is the IP address of the datagram sender.

DatagramLength Field

DatagramLength is the length of the datagram in bytes.

DatagramPort Field

DatagramPort is the sender's port number from which the datagram originated.

Message Field

Message is used by the error event to store the descriptive message that is generated when an error occurs.

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Example: Using Events and Callbacks

This example extends Example: Communicating Between Two Hosts to include a datagram received callback. The callback function is instrcallback, which displays information to the command line indicating that a datagram has been received.

The following command configures the callback for the UDP object u2.

u2.DatagramReceivedFcn = @instrcallback;

When a datagram is received, the following message is displayed.

DatagramReceived event occurred at 10:26:20 for the object: 
UDP-doetom.dhpc.
25 bytes were received from address 192.168.1.12, port 8844.

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Writing and Reading Data

Using Device Objects

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