Transponder Mode

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The transponder is synchronizing with the FltSim XPDR code. However, unlike our X-Plane version, the transponder mode is not synced with FltSim just because there is no XPDR mode in FltSim (it is assumed always ON and there is no SDK variable). To enhance the capabilities of our GTN, we're publishing our own XPDR mode simvar (along with IDENT and LIGHT simvars) to permit third party gauges/modules to interact with our GTN XPDR.

Also, in our X-Plane version, there are further multiplayer support via PilotEdge and VATSIM, which permit displaying the RX/TX COM flag when communicating. There is none of this in our FltSim version yet simply because we can't get a hold on Keith (PilotEdge) for the last 6 months, nor it is clear at this time if any of third party online network clients are sharing any data to third parties for such integration. If you have further information on this, we'll be glad to evaluate!

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Bumping this thread:

For us who use vPilot this is from the vPilot documentation,


 If the add-on aircraft you are flying has SquawkBox transponder integration, then vPilot will detect transponder mode changes when you toggle the mode using the aircraft panel within the sim. If this happens, you'll see the Mode C button on the vPilot main window light up in green when the transponder is in Mode C.

And from the older squawkbox documentation for FSUIPC offsets,


SquawkBox Specific Offsets

Offset Size (in bytes) Description SquawkBox reads? SquawkBox writes?
0x7b91         1                                                           Transponder mode
0 = normal
1 = standby
SquawkBox reads this value to determine which transponder mode to send to the network. Your transponder gauge should set this offset when the user changes modes with your gauge.
0x7b92 1 ATC activity indicator. This value is normally set to 0. When SquawkBox receives a ping from a nearby ATC, it sets this value to 1. If you want your gauge control to flash your ident light you should check this value periodically. As soon as you notice the value is set to 1, you must reset it to 0. NO YES
0x7b93 1 Transponder Ident pressed. When the user presses the ident button on your transponder gauge, you should set this value to 1. When SquawkBox notices it is set to 1, it will transmit an ident on the network and reset the value to 0. YES YES


And for my A2A aircraft which don't have squawkbox integration built in I use a LUA script found on the web:

function sqmode(varname, value)
	avi_swtch = ipc.readLvar("AvionicsElecPower")	
		if avi_swtch==1 and (value==4 or value==3) then
			--squawk mode charlie
			ipc.writeSB(0x7B91, 0)
			--squawk mode stand by
			ipc.writeSB(0x7B91, 1)
		--squawk mode stand by
		--ipc.writeSB(0x7B91, 1)

function sqident(varname, value)
	if value==1 then
	--squawk ident
		ipc.writeSB(0x7b93, 1)

event.Lvar("L:xpdr_onoff_knob_pos", 500,"sqmode")
event.Lvar("L:xpdr_ident_button", 500,"sqident")


The question for RXP is then:

Are there any variables in the GTN that can be used to implement this functionality, or update the LUA script?
Otherwise, would it be very problematic to implement the variables, or make the software write the SB values?

As you can see from the SB documentation there is also an offset for flashing the Ident light to simulate radars interrogating the transponder, (not sure if this is implemented in vPilot, but I see in the GTN manual that there is a rxp varable for this already 🙂 )

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The RXP GTN already publishes variables for this (see p13 User's Manual):  boolean  (squawking if true)
rxp.transponder.light boolean (replying if true)
rxp.transponder.mode enum (STBY=0,ON=1,GRND=2,ALT=3)

You can write these vars and the GTN will work accordingly (supposedly!)

However, we'll never support any FSUIPC interface. Third party vendors can easily open their online clients via L:vars (like we do).

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