Originally Posted by JDA_BTR
Different drawings show different things too.
Should the GSU25 backup serial port go to the PFD, or the GTX45R? Seems the GTX is a better choice since that keeps ADSB going even on a CAN bus or PFD failure? The GTX would be getting GPS via ethernet in that mode still.
Should a serial GTN->GTX link be provided for backup even when an ethernet is cabled in?
The GSU 25 ADAHRS to GTX 45R transponder interface is a single RS-232 interface and is shown on page 26-22 of the Rev. AB installation manual. This interface has absolutely nothing to do with a GSU 25 backup data path.
The GSU 25 RS-232 backup data path to a display (PFD1 recommended) is shown on page 26-9. There is no such thing as a GSU 25 backup data path to a GTX.
The Ethernet interface between the GTN and GTX 45R shown on page 26-22 is a bi-directional link that both provides ADS-B+ data to the GTX 45R enabling it to provide ADS-B Out and provides ADS-B traffic/weather data from the GTX 45R to the GTN.
We don't recommend both
the Ethernet interface and an RS-232 interface to get GPS data from the GTN to the GTX and haven't tested that, but it might work.
Just follow those two wiring diagrams on those two pages and you can't go wrong.