Hey Boon,
Have you considered using data lines to send the high or low signals to the transceivers? You have not mentioned how many of the 655x's data lines you are using for the actual data to the DUTs (Device Under Test). So one option would be that you can set up 4 of your data lines to be static generation and then toggle them as needed. Since there are 20 data lines on the 655x, you could for example use lines 0, 5, 10, 15 as your static lines, and then 1-4, 6-9, 11-14, 16-19 as your data lines, which would give you 4 data lines and 1 static per DUT. This is assuming that you only have one board. The only way that this might not be possible is if you are using 5 data lines per DUT, which would use up all of the data lines.
Which brings up some good questions: How do you have your data lines and overall system configured? Or how do you plan on writing/reading data to/from your 4 DUTs? Do you just have one 655x or multiple? Does your Transceivers send any data back that also tells the board when it is transmitting or receiving (an output line)? Is this system going to be doing some kind of "handshaking"? What kind of rates (how fast) are you going to be sending and receiving data (50 MHz, 100 MHz, other)?
So some other methods that you can consider in order to use the PFI lines to do static generation would be to use Triggers or Events. One possible method would be using a Pause Trigger, which you could then route to the PFI Line(s) that you want. In the NI Digital Waveform Generator/Analyzer Help document it says the following on the "Triggers Summary" page: "The Pause trigger indicates to the device that it should pause the acquisition or generation. Therefore, the Pause trigger is only effective when received during an active acquisition or generation session. For generation operations, the Data Active event indicates when the operation is paused." Also, if you check out the "Dynamic Generation Triggers and Events" page, you will see that it says that: "The Pause trigger can be exported to PFI <0..3>".
So an event that you can use is the Data Active Event, and you can route that to the PFI lines. In the help it says: "The Data Active event indicates when the Pattern Generation Engine is generating data. If the Pattern Generation Engine is waiting for a trigger or is paused, the Data Active event is deasserted. When the Pattern Generation Engine is generating data, the Data Active event is asserted, synchronous with the data." An example that routes the Data Active Event is the "Dynamic Generation and Acquisition - Source Synchronous.VI" that can be found in the NI Example Finder in LabVIEW. Now if your DUT needs some time to configure itself after it changes from send or receive, then you can adjust for that in your data that you are sending it, by adding some dummy data in the beginning of the waveform, before the device is ready to receive the data.
There might be some other possibilities, like Marker Events, Ready for .... Events, and Scripting with script triggers, which you can also read up on all of these in the help documentation. I hope this helps. Please let me know if you have any further questions or concerns. Thanks, and have a great day.
Regards,
DJ L.