I would like to know if RS 232 signal is sufficient to feed the GPSS. At
this day I didn't get any answer,even from BendixKing.
By the way,should you know if the P 891 # 6 pin can be used to transmit a
signal to an autopilot (it is labelled"Spare RS 232 output) or if I can feed
a KMD 250 AND a Trutrak autopilot  (both) from the P 891 #2,labelled
"General RS 232 Output" ?
Many thanks.

Alain,

 

To be clear, ARINC sends steering data that can be interpreted and converted into turn commands just like turning the bug on the DG.  RS232 sends NMEA 185 (or similar) text data sentences containing lat/long and, if produced by the GPS, course deviation data, etc. The Autopilot would have to convert course deviation to alter the flight path of the airplane just like it interprets VOR course deviation information.

 

Most GPS's produce the NMEA data that is where you were or how far off you are - after the fact.  The brainless autopilot tries to reduce the track error.  The GPS can tell you a turn is coming up but cannot make the turn.  This is GPS NAV Mode.

 

The ARINC turning data is used to command the airplane to go somewhere in the future - fly a turn before crossing the way point, follow an approach arc, fly a GPS approach, etc.  It is up to the computations in the GPS to tell the autopilot where to guide the airplane.  This is GPS steering mode (and in some cases, vertical steering also - See GSX80).

 

See the chart on:

 

 

Look at the wiring diagram at the end of

 

 

Note that the inputs are

 

serial from GPS (that's RS232)

2 ARINC steering inputs (if you have them)