===== Q: I receive an error about invalid PD from iol-master-appl =====

<code>
[12:53:29 WARN ] generic_run0: PDIn data is invalid for port 1
or 
[12:48:33 WARN ] generic_run0: Failed to get PDIn from port 1, len requested=4, len act=2
</code>

===== A: To exchange process data (PD), both PDIn and PDOut have to match the device =====

Process data is exchanged automatically in the background as soon as the connected device is powered. If the PD has never been set by a [[..:sw:3_binary-protocol:3.3_cmd-pd|PD command]], the PD is marked as invalid (''PDIn'' and ''PDOut'' length = 0). 

The length of the PD is reported back from the device on connection. If there is a mismatch between the set and reported length, the PD fails to match.

<WRAP info>
Per SDCI specification, the PD is always fully exchanged (send full ''PDOut'', receive full ''PDIn''). 
</WRAP>