Garmin 396 - SL40 and Trutrak

I'm replacing my GNC250XL with an SL40 and a Gramin 396/496. I'm currently feeding my Trutrak Pictorial Pilot with the 250. It's my understanding that the 396/496 will feed the Trutrak Autopilots and I know they will feed the SL40. I found out the hard way that my 296 wouldn't feed the SL40, but that just gives me a good reason to upgrade.

The question I have is will the 396/496 feed both the Trutrak and SL40? From the 396 manual I see there is a setting for "NMEA and VHF out" so it looks like it will work. Has anyone done this?

Thanks.

flymustangs said:

I found out the hard way that my 296 wouldn't feed the SL40, but that just gives me a good reason to upgrade.

Thanks.

Click to expand...

Garmin supposedly fixed this recently with their operating system update to version 4.0 (now at ver 4.4)
From their website:
Changes made from version 3.70 to 4.00:

* Added support for tuning SL30/40 comm radios through 'Aviation In/NMEA & VHF Out' serial interface format.

Have you upgraded your operating system on the 296 and it still doesnt work?

Regards,
Tom Velvick
RV-4

Tom,

Thanks for the help. I didn't think about checking for software updates that would add this feature because I just talked to the Garmin AT folks last week. They "confirmed" that the 296 wouldn't send freqs to the SL40. I guess you can't expect them to know everything about every Garmin product.

I just updated my 296 to v4.40 and it does show the "NMEA & VHF Out'" options now. Can't test to make sure it works until I get it hooked up to the SL40.

I guess I need to modify my question and ask will the 296/396/496 feed both the SL40 and a Trutrak AP at the same time?

Thanks.

flymustangs said:

I guess I need to modify my question and ask will the 296/396/496 feed both the SL40 and a Trutrak AP at the same time?

Click to expand...

Yep - you just need to use the "NMEA & VHF" output mode.

mcb

flymustangs said:

The question I have is will the 396/496 feed both the Trutrak and SL40? From the 396 manual I see there is a setting for "NMEA and VHF out" so it looks like it will work. Has anyone done this?

Thanks.

Click to expand...

My 396 talks to both my SL30 and TT DF200VS. No probs.

"at the same time"

I hope I am not answering at too basic a level, but all you have to do is physically Y the output wire because it's a serial connection. It would feed three gizmos if you wanted. I did have a problem with using both output ports on my 296 in the same format at the same time, though.

Because it's serial is exactly why I asked the question. I was pretty sure it would drive three devices as far as power goes. I think that's fairly standard for a serial device. The question was on the data content itself.

The Garmin doesn't care how much information it puts out on that serial connection. The question is on the devices receiving the information. I did have one problem several years ago where the receiving device wouldn't work correctly because there was additional information in the data stream that the device couldn't intepret correctly and wouldn't ignore for some reason. I didn't think that would be an issue here because the SL40 information complies with the NMEA standard, which shouldn't care if additional sentences are added to the stream. I just wanted a second opinion.

The other issue is the amount of data. If you're packing a bunch of information into the stream it could delay updates to the autopilot making it potentially less responsive to changes. The 296 and probably the 396 and 496 have an option to modify the NMEA stream to improve the update rate, but I don't know if that can be done while retaining the necessary information for both the Trutrak and the SL40. I'll have to do some more research and some testing when I get them installed.

With the 296 the answer might be to use both outputs, one for the SL40 and one for the autopilot. That would require a wiring change later if I chose to upgrade to a 396 or 496.

Thanks.

flymustangs said:

With the 296 the answer might be to use both outputs, one for the SL40 and one for the autopilot. That would require a wiring change later if I chose to upgrade to a 396 or 496.

Thanks.

Click to expand...

Please let us know if you can do it. When I tried to use COM 1 and COM2 both configured the same, my 296 would not do it. I would have preferred that to the Y connection. It seemed to want the two ports to have different configurations. I have no idea why. Maybe they have fixed it. I am two releases behind on their firmware.

Related but not the same issue: For the TruTrack, I installed a switch so that it can receive directly from the Garmin or receive GPS data through my GRT EFIS, which is functionally preferable. Right now, the GPS data in the EFIS is from the Garmin 296, but that switch both allows me to use the AP if the EFIS fails and also allows an additional or different GPS anywhere in the system. Just FYIO.