All inputs on done on the panel right below the HUD, or the ICP.
With the DED on the main page (to get here LEFT click on the RTN/SEQ switch). This page displays all your COMM and NAV data, known as the CNI page:
UHF xxx.xx STPT1
VHF xxx.xx TIME
Xpnder TACAN
Click button 4/STPT, the DED should display the STPT menu. We'll stay with STPT 1, as it's the first to display.
RIGHT click on the RTN/SEQ switch, a * * should appear around the N, this means you are in the scratchpad mode.
Click on the 2 button to select North (N), the ** should move to the first "0", type in your latitude, click ENTR.
Now the ** will be on the second set of numbers on the DED, "xx.xxx", type in your numbers, you may need to add a "0" at the end, click ENTR.
Repeat the process for West or East, after you enter the last of your longitude, click ENTR.
At the bottom of the DED, **ACTIVATE** will appear, click ENTR.
Down on your HSI, move the mode switch over to NAV and check your range/bearing.
To cycle STPT's, the up/down arrow button on the ICP can be LEFT/RIGHT clicked.
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Again using the RTN/SEQ switch, get into the main DED menu. Click on the 1/T-ILS button, this brings up the TACAN/ILS menu on the DED.
RIGHT click the RTN/SEQ switch, you will get the ** again, the left set of numbers is your VOR freq to add as a TACAN. RIGHT click the RTN/SEQ again if you want the ILS on the right, the course below does nothing, only the course on your HSI.
Manual is in your main FSX folder under IRIS Pro Series.