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Garmin GPS175

Posted: Thu Sep 10, 2020 6:46 am
by GRT_Jeff
The new GPS175 is designed to interface like the previous GNS430 and GTN650. The 175 is GPS-only. It doesn't have a com radio or VOR/ILS receiver.

Here are some notes on wiring and configuring.

The GPS175 pins are on the J1751 connector.

RS-232 connection
GPS175 Pin 9 (RS-232 OUT 1) -- any serial input on EFIS
Example 1: GPS175 Pin 9 (RS-232 OUT 1) -- HX/HXr/EX/10.1 pin A22 (Serial 5 IN)
Example 2: GPS175 Pin 9 (RS-232 OUT 1) -- SX pin 30 (RX1)
Example 3: GPS175 Pin 9 (RS-232 OUT 1) -- GRT ARINC pin 8 (Serial Input pass-thru on male DB9 on box)

A direct connection to the display is preferred unless you're out of serial ports.

ARINC connections
The GRT ARINC-429 connector (female DB9 on external module box or back of HX/HXr) will be referred to as the C connector here.
GPS175 Pin 5 (ARINC 429 OUT 1A) -- GRT ARINC pin C1 (ARINC 429 IN 1A)
GPS175 Pin 6 (ARINC 429 OUT 1B) -- GRT ARINC pin C2 (ARINC 429 IN 1B)
GPS175 Pin 27 (ARINC 429 IN 1A) -- GRT ARINC pin C5 (ARINC 429 OUT A)
GPS175 Pin 28 (ARINC 429 IN 1B) -- GRT ARINC pin C9 (ARINC 429 OUT B)

(Any other RS-232 input/output and ARINC-429 input/output can be substituted.)

GPS175 Settings:

ARINC RX Port 1:
Format: EFIS/ADC
Speed: Low

ARINC TX Port 1:
Format: GAMA Format 1
Speed: Low

RS232 Port 1: Aviation Output 1

The 175 does not have an RS-232 Fuel/Air Data (FADC) input like other Garmin IFR GPS units.

EFIS Settings in SET MENU, General Setup:

For units with external ARINC module: ARINC Module Connected: Yes, Port (select port it's wired to)

ARINC Receive Rate: Low
ARINC Transmit Rate: Low

Serial Port Rate: 9600
Serial Port Input: GPS1 Aviation/MapCom
The Serial Port Output is not used for the 175 and can be used for unrelated functions at 9600 baud.
Using GPS1 for the GPS175 is recommended and sometimes required. Change any other GPS to GPS2.

If the GPS RS-232 is connected to the pass-thru port (pins 8 and 9) on the external ARINC module male DB9,
configure the serial port that the ARINC module is connected to as 9600 GPS1 Aviation/MapCom.

For example, if the ARINC module is connected to port 4, the settings would look like this:
ARINC Module Connected: Yes, Port 4
Serial Port 4 Rate: 9600
Serial Port 4 Input: GPS1 Aviation/MapCom

Other settings in General Setup:

This tells the EFIS to use the GPS data from the ARINC-429 connection when GPS1 is selected.

NAV Mode Source: Internal
The GPS175 does not have a built-in VOR/ILS receiver, so all mode changes must be done in the EFIS.

GPS1 Flight Plan Source: External
This tells the EFIS to use GPS flight plan data from the GPS175 RS-232 connection.

GPS2 Flight Plan Source: update this to match your GPS2, if any.
GRT GPS units should be Internal. GPS units that transfer flight plan data should be External.

Virtual GPS2: Normally Off unless you know you want this feature.
If you have two GPS inputs this must be Off.

Settings in SET MENU, Primary Flight Display:

To enable the approach modes and PFD indicators, you must configure the ILS display:

ILS Type: pick Needles or Scales as preferred
When some other features are turned on, only Scales mode is possible.

Show VOR CDI on Localizer: No, unless you have a VOR input.

Show GPS CDI on Loc/GS: Yes
This displays the GPS approach deviations on the ILS indicators.
This is required for the GPS approach display and capture modes in the EFIS.

Re: Garmin GPS175

Posted: Tue Oct 13, 2020 9:55 pm
by minnimo65757
Pin 48 and 49 is ARINC 2-IN A&B should it also be connected to Pin 3 & 4 of the ARINC module or leave 3 & 4 open. Pin 8 & 9 of the other connector is the Expander serial out and in and it say to go to Avionics serial out and in. What would be an example of avionics serial out and in be? I have a TruTrak Gemini auto pilot would that be where that would connect? Or does the autopilot connect to the EFIS but work through the ARINC somehow? Anyway your help would be appreciated on this.

Re: Garmin GPS175

Posted: Wed Oct 14, 2020 11:57 pm
by GRT_Jeff
Pins 3 and 4 are another receive channel on the ARINC module. You won't be using those pins. Normally they are used for the VOR/ILS output of a 430W or similar unit.

Pins 8 and 9 on the other connector are optional in case you are out of RS232 serial ports on the display and need to connect something low-speed (max 19200 baud).

TruTrak autopilots with ARINC-429 connections require both an RS-232 input and ARINC-429 inputs. Usually the TruTrak RS-232 input connects to the GPS output, and the TruTrak ARINC-429 input connects to the EFIS ARINC-429 output. These are shared connections when something like the GPS175 is involved. For example the RS-232 output of the GPS would go to both the EFIS and the TruTrak. The ARINC-429 output from the EFIS would go to both the 175 and the TruTrak.