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GRT to G430 Wiring

Pilotjim77

Well Known Member
Hi All,

GRT has a wiring diagram showing the pin connections for a G430.

http://grtavionics.com/media/Horizon-430W.pdf

In the drawing, there is a 12v input with 10k resistors to pins 18-21 on connector B. These also connect to the G430 pins 1,2,7 on P4001 and pin 29 on P4006. I don't understand this because I thought the 430 had it's own required 12v power. Can anyone tell me what this 12v power input is for?

Just trying to understand how this works and why. Thanks for any assistance.
 
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Pull up resistors in GRT wiring diagram

The resistors connected to +12v are what are typically called pull up resistors. The Garmin 430 pins are discrete logic “outputs” that are either open circuit or pulled to “ground” by the Garmin 430. In order for the the GRT EFIS to correctly sense these signals it needs them pulled high (+12V) or low (ground). The resistors are sized such that there is minimal current drawn from the +12V power when the Garmin unit grounds that output.
 
In addition, newer (e.g., HX but not HS) GRT models have these pull up resistors already installed, internally. You have a choice, in the software setup for each RS232 port, for ‘pull up on’ or ‘pull up off’ or something like that.
 
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