UDP Warning - Unable to Read Any Data
These remedies apply to the case when you receive no data and you get this warning message:
'udp' unable to read any data
ASCII and Binary Data
When using the UDP interface for:
Reading ASCII (text) data using the
fscanf
,fgets
, orfgetl
functionsReading binary data using the
fread
function
these are possible causes and remedies:
Cause | Solution |
---|---|
An invalid command was sent to the device, so there is a problem reading the response to the command. | Check your device manual for proper command formatting. |
The device did not receive the command because of an incorrect UDP
RemotePort value. | Verify that the UDP RemotePort value is set to the
port number the device is listening on. For more information about
setting the remote port, see udp and Create a UDP Object and View Properties. |
A firewall is blocking incoming UDP packets. | Verify that your system firewall setting allows connections to 'LocalPort'. |
The UDP packet size is larger than the maximum packet size that can be handled by the Ethernet adaptor. | The UDP packet size is controlled by the
OutputDatagramPacketSize property. You can
specify the size, in bytes, between 1 and 65,535, and the default value
is 512. |
You might need to enable port sharing. | If you are receiving UDP broadcasts on a shared port, set the
EnablePortSharing property to
on . For the syntax, see "Enable Port Sharing Over
UDP" in Create a UDP Object and View Properties. |
Binblock Data
When using the UDP interface for:
Reading binblock (binary-block) data using the
binblockread
function
these are possible causes and remedies:
Cause | Solution |
---|---|
An incorrect write terminator was sent to the instrument before attempting to read data, so there is no data to read. | Verify that the Terminator property is set to the
value required by your device. |
An invalid command was sent to the device, so there is a problem reading the response to the command. | Check your device manual for proper command formatting. |
The device did not receive the command because of an incorrect UDP
RemotePort value. | Verify that the UDP RemotePort value is set to the
port number the device is listening on. For more information about
setting the remote port, see udp and Create a UDP Object and View Properties. |
A firewall is blocking incoming UDP packets. | Verify that your system firewall setting allows connections to 'LocalPort'. |
The UDP packet size is larger than the maximum packet size that can be handled by the Ethernet adaptor. | The UDP packet size is controlled by the
OutputDatagramPacketSize property. You can
specify the size, in bytes, between 1 and 65,535, and the default value
is 512. |
You might need to enable port sharing. | If you are receiving UDP broadcasts on a shared port, set the
EnablePortSharing property to
on . For the syntax, see "Enable Port Sharing Over
UDP" in Create a UDP Object and View Properties. |
If the amount of data being received spans multiple UDP packets, it is possible that the system dropped packets. | The UDP packet size is controlled by the
OutputDatagramPacketSize property. You can
specify the size, in bytes, between 1 and 65,535, and the default value
is 512. You can increase or decrease the packet size if
necessary. |
More Troubleshooting Help
For more information about troubleshooting the UDP interface, including supported platforms, adaptor requirements, configuration and connection, and other troubleshooting tips, see Troubleshooting UDP Interface.