L-1011 Trainer Installation: SFENA HSI Installation Preparation and ARINC 429 Bus Integration

For the ARINC 429 integration of the L-1011 trainer at the museum we will be using bus interfaces made by V1 Avionics. For the integration testing V1 Avionics used the museum's L-1011 HSIs and ADIs. The video below shows the instrument preparation and testing prior to installation into the L-1011 trainer. The L-1011 sim will use the following ARINC 429 capable instruments:

1. Attitude Director/Indicator (ADI)
2. Horizontal Situation Indicator (HSI)
3. Altimeter (ALT)
4. Vertical Speed Indicator (VSI)
5. Inertial Navigation Unit Display (INU CDU)
6. Datalink Display Unit (DU)
7. Performance Management Unit (PMU)
8. Communication Radio Faces (COM1/COM2/COM3)
9. ATC Transponder (ATC)

L-1011 Avionics Bending: SFENA HSI and ARINC 429 - Part 15 (Final)

In this last video for the ARINC 429 integration of the SFENA HSI with Laminar Research X-Plane I get a chance to demonstrate the dual HSI setup in flight. The software now allows for the Captain and the First Officer to select different display data as well as different (simulated) instrument sources. The video below concludes the deep dive into the HSI and next we will be looking into integrating the L-1011 Tank Panel and Altimeter.

The video today shows a short demonstration flight out of Seattle-Tacoma International airport using x-plane 10. The ARINC 429 Labels integrated for this video are:

Label 320, 012, 101, 162, 222, 100, 

      314, 114, 116, 117, 001 and 270

L-1011 Avionics Bending: SFENA HSI and ARINC 429 - Part 14

SFENA HSI - Dual Setup - ARINC 429

Now that one of the HSIs is working fine I am looking into integrating both the Captain's HSI as well as the First Officer's HSI with the Flight simulator. The cool thing is that because of the ARINC 429 protocol we really only need a total of 3 channels to simulate the 12 channels that instrument required when it was deployed on the actual aircraft.

Below is a short video the shows both HSIs receiving the same ARINC 429 test data. The data labels sent to the instruments for the test are:

• Label 320 .. Magnetic Heading as a full 360º circle
• Label 100 .. Selected Radial as a full 360º rotation
• Label 222 .. Omnibearing from a VOR in a full 360º circle

During the roll of the Radial and the Omnibearing the TO/FROM pointers are changing directions as the simulated VOR moves from the front to the back of the simulated aircraft.

L-1011 Avionics Bending: SFENA HSI and ARINC 429 - Part 13

The next stop on the ARINC 429 label integration between x-plane and the SFENA HSI is ARINC 429 Label 162 for the Automatic Direction Finder (ADF). The ADF is a relatively basic but very powerful instrument. What it does, in essence, is that it points to a Non-Direction Beacon (NDB). It does so, relative to the nose of the aircraft. Well, you know how an ADF and NDB works .. i don't need to go into too much detail here. From an integration perspective, it is important that the HSI shows the bearing to the NDB correct with respect to the aircraft nose ... regardless of the actual magnetic or true heading of the aircraft.

The video below shows the integration of ARINC Label 162 which is encoded as a BNR and uses the same 32bit word encoding I showed you in my blog posting a few days ago that explained BNR as a data payload in the ARINC 429 word.

NDB navigation is fun but can be a bit tricky. I promise that once the simulator is all put together we will fly some non precision approaches using an NDB! By the way, the airport code for San Francisco International is of course KSFO not KFSO as i wrongly stated in the video :)

L-1011 Avionics Bending: SFENA HSI and ARINC 429 - Part 12

Today's posting is all about integrating the FMS in to the HSI as the primary NAV instrument. Of course, on the L-1011 this would have been the INS or OMEGA. For the HSI demonstration today I am using the generic FMS in x-plane. The NAV mode of the HSI requires the following ARINC 429 labels to be integrated:

1. Magnetic Heading and/or True Heading (BNR)
2. NAV Course (BNR)
3. NAV Horizontal Deviation (BNR) 
4. NAV Vertical Deviation  (BNR)
5. Ground Speed (BCD)
6. Distance-To-Go in Nautical Miles (BCD) 

So, all in all quite a lot of different parameters. Each of the values is presented by x-plane and the SDK as a floating point number and requires the correct translation into either BNR or BCD format. If you are curious about the BNR encoding you can take a look at my previous post which shows how I convert the x-plane dataref to an ARINC 429 compatible BNR.

The video below demonstrates a takeoff from Seattle-Tacoma International Airport (KSEA) on a direct course to San Francisco International Airport (KSFO).

L-1011 Avionics Bending: SFENA HSI and ARINC 429 - Part 11

The work on the SFENA HSI continues. By the way, SFENA later became Sextant Avionique which then became part of the french Thales Group. Awesome products and very neat engineering that went into this device. In the video below you can see the integration of the following X-Plane parameters

1. Magnetic Heading
2. VOR OBS Setting
3. VOR Omnibearing
4. Autopilot Heading Select 
5. Ground Speed 

There are a few more ARINC 429 labels to go but I do think that I will have pretty much all the components working by the end of the week. Then its on to the fun stuff ... making the HSI work with alternate, pilot selectable, sources and driving both the pilot as well as the first officer's HSI from X-Plane.

L-1011 Avionics Bending: SFENA HSI and ARINC 429 - Part 10

Good progress on the SFENA HSI integration work. All software pieces are now in place and the HSI can be controlled via x-plane.

HSI Software Integration

While today's posting does not integrate all of the ARINC 429 labels required to run the entire instrument, it uses Label 320 which describes "Magnetic Heading from AHARS".  For the magnetic heading data to arrive at the HSI the following steps have to be taken:

1. The magnetic heading data is extracted from the x-plane flight simulator and stored in a shared memory segment by the TAP process as a floating point number.
2. The ARINC 429 to UDP subsystem picks up the float and converts it to an ARINC 429 encoded BNR. The parity for the ARINC 429 data is computed and the data together with the label sent on via UDP to the HSI driver
3. The HSI driver takes the label and the already ARINC 429 converted data from the UDP packet and queues it to the ARINC 429 adapters high-speed (100Kb/sec) transmit channel
4. The HSI logic translates the data into motor movements and rotates the heading hard to the correct position

All of the above happens once every 50ms to create a smooth movement of the HSI instrument.

The video below is a short demonstration of the end-to-end integration of the SFENA HSI:

Over the next few days I will work on the complete integration of all the data needed to operate all the features of the SFENA HSI. 

L-1011 Avionics Bending: SFENA HSI and ARINC 429 - Part 9

Worked on the data transfer between the ARINC 429 Subsystem with UDP software and the HSI driver component.

In the video below you can see a sequence of Label 320 (Magnetic heading from AHARS) test data being sent via UDP from the ARINC 429 Subsystem to the HSI Driver.

The next step will be to connect X-Plane itself to the shared memory segment. This work will start tomorrow. Again, I will post the code (and a link to github) for all this at the end once the HSI is fully integrated.

L-1011 Avionics Bending: SFENA HSI and ARINC 429 - Part 8

The systems design for the SFENA HSI integration calls for a number of discrete I/O pins to be handled via a National Instruments DAQ card. The card that I use for this setup is an older PCI-DIO-96 card. The TTL level I/O on the card controls a set of relays supplying 24VDC to the discrete pins on the SFENA HSI.

HSI Integration of 24V Discrete Channels

The video at the top of the blog posting shows the operation of the relays via the NI card. The SFENA HSI supports the following discrete inputs:

SFENA HSI Discrete Input

The instrument specification actually asks for a range between 18.5VDC and 28VDC as the "hi" value for the pin, therefore, the 24VDC source that I use is well within the design limits. 

L-1011 Avionics Bending: SFENA HSI and ARINC 429 - Part 7

Today I am planning the code for the SEFNA HSI integration. As I described in my previous posting there are a three programs that will make up the HSI integration, they are: a) The Avionics Plugin in X-Code (TAP), b) the ARINC 429 Subsystem with UDP and c) the HSI device driver. Here is a more detailed description each oft he elements:

1. The Avionics Plugin (TAP)

Simplified TAP Flowchart

The TAP plugin, as describe above, is meant to be very light weight on the simulator and should show a minimal impact on the frame rate produced by the simulator software. The code, in essence, extracts data and stores it away in a shared memory segment, upon update, the code also pulls a shared semaphore to indicate to the downstream process that the shared memory segment has been updated and processing is required. X-Plane has a really neat plugin facility that allows for dynamic loading and un-loading of the plugin.

Getting the data out of the simulator frequently and quickly will be essential to creating a smooth presentation of the data on the physical device. Therefore, I plan to offload the data from the flight simulator at a rate of 20 times per second or an update refresh time of 50ms. Of course this will not result in a 50ms refresh cycle all the way on the hardware device, since there are two more downstream programs and network latency to be considered. (More on computing, or pre-computing, the latency in my blog post tomorrow)

2. ARINC 429 Subsystem with UDP

Simplified ARINC 429 with UDP Flowchart

The ARINC 429 Subsystem runs on the same system together with the core flight simulator software. The subsystem attaches itself to the same memory segment as TAP and waits for data from TAP. The X-Plane and Microsoft Flight Simulator FSX data is not in the correct format for ARINC 429 words. For example, angular data (such as heading) is described as a "float" number by X-Plane, however, the ARINC standard describes angular data in twos complement fractional binary notation (BNR). Once the data has been converted to the correct format it is made available on the Ethernet network via a UDP data stream. Clients, such as the HSI Device driver described below, will be able to connect to a specific UDP socket and receive the necessary data already in a format to be handed of to the local ARINC 429 hardware adapter.

The ARINC 429 conversion happens as soon as the TAP application raises the shared semaphore. So, at best new data is loaded into the shared memory segment every 50ms and has to be processed and put on the Ethernet in less than 50ms in order to be ready for the next data element to be worked on.

3. HSI Device Driver

Simplified HSI Driver Flowchart

The HSI device driver knows how to operate the specific device. So, to be exact, this is really the SFENA HSI device driver. Receiving words from the ARINC 429 Subsystem with UDP on the system that runs the flight simulator, the HSI device driver schedules the necessary ARINC 429 words on the 429 capable hardware and also sets digital I/O lines on the DI/O hardware.

The HSI drivers response time is really driven by a number of variables: a) the time it takes for the device driver to receive and assemble the UDP packets into a complete dataset, b) the time to schedule and/or update the ARINC 429 word on the hardware adapter and c) the time it takes for the driver to set the necessary digital I/O channels. Here, again, it will be critical to hold latency down to a minimum. 

L-1011 Avionics Bending: SFENA HSI and ARINC 429 - Part 6

Proposed Integration of the SFENA HSI with Laminar Research X-Plane 10

The schematic above shows my initial approach to integrating the HSI with the X-Plane software platform. There are several shared code pieces that I also use for other hardware integration efforts. The following code elements are shared:

• The Avionics Plugin (TAP) - that is my data extraction tool for pulling X-Plane datarefs out of the simulator and storing them in a shared memory segment
• ARINC 429  Subsystem - takes information out of the shared memory segment, does data transformation from the X-Plane data format to the ARINC 429 compatible data format (e.g. BNR and BCD) and sends it on to the receiver via UDP

On the receiver side there is a need for data being sent in the ARINC 429 Fast and Slow standard as well as a number of 24VDC discrete switches to control the HSI states. For that I will use the DDC DD-42924i5 device driver and SDK kit as well as the National Instruments DAQmx device driver SDK.

L-1011 Avionics Bending: SFENA HSI and ARINC 429 - Part 5

So now that we have walked through the major function blocks of the SFENA HSI it is time to think about integrating it with a flight simulator. For this device I will use X-Plane 10 by Laminar Research. As you probably know, the X-Plane platform can output data in a number of ways. Perhaps the easiest way is to simply let the software stream some data via UDP to another computer that the HSI is attached to. However, I will use a different method that will use a X-Plane plugin written in C that will offload the work of sending the data to the HSI to an external device driver ... therefor, keeping the computational demand on X-Plane as minimal as possible while preserving the maximum frame rate.

In particular we will be using at the following data points:

X-Plane 10 Screen Shot of Data Sources

In order to get to all of the parameters I need I will use the SDK for X-Plane and stream the data via the data references (aka. datarefs) exposed by the SDK. So, lets match up some SFENA HSI ARINC 429 labels with X-Plane 10 datarefs (the previous link is valid as of the time of the posting, however over time it might expire and/or change).

ARINC 429 Label: 320    
Function:  Magnetic Heading    
Dataref: sim/cockpit2/gauges/indicators/heading_electric_deg_mag_pilot

ARINC 429 Label: 321
Function: Drift
Dataref: sim/cockpit/gyros/dg_drift_ele_deg

ARINC 429 Label: 012
Function: Ground Speed IRS/AHRS
Dataref: sim/flightmodel/position/groundspeed

ARINC 429 Label: 101
Function: Heading Select
Dataref: sim/cockpit2/autopilot/heading_dial_deg_mag_pilot

ARINC 429 Label: 162
Function: ADF 1 Bearing
Dataref: sim/cockpit2/radios/indicators/adf1_relative_bearing_deg
and/or
Dataref: sim/cockpit2/radios/indicators/adf2_relative_bearing_deg

ARINC 429 Label: 222
Function: Omnibearing
Dataref: sim/cockpit2/radios/actuators/nav1_obs_deg_mag_pilot

ARINC 429 Label: 100
Function: Selected Radial
Dataref: sim/cockpit2/radios/actuators/nav1_course_deg_mag_pilot

ARINC 429 Label: 173
Function: Localizer
Dataref: sim/cockpit2/radios/actuators/nav1_course_deg_mag_pilot

ARINC 429 Label: 174

Function: Glide slope

Dataref: sim/cockpit2/radios/indicators/nav1_vdef_dots_pilot

There are additional labels to follow in the next posting. The HSI will also need a number of discrete lines that need to be switch by X-Plane via a 24V relay. 

L-1011 Avionics Bending: SFENA HSI Power Up and ARINC 429 Test - Part 4

The magnetic wheels used in the SFENA HSI are in itself a pretty neat thing. Prior to the use of magnetic wheels digit drums had been driven by gear linkages and motors. Magnetic wheels work by rotating a drum with a magnet and digits printed on the outside around 10 positions that can be individually energized. By doing the former, the display can show single digits ... one at a time and, they are perfectly silent.

The magnetic wheel allowed for a much more simplified way of showing digital data without the need to create complex motor mechanisms. Below is a video that shows the 10 position magnetic wheels in the SFENA HSI instrument in more detail. Each digit in the 5 digit distance-to-go is a unique magnetic wheel:

Both ground speed as well as distance-to-go use magnetic wheel technology. Of course, later on magnetic wheels got replaced with 7 segment LED displays.

L-1011 Avionics Bending: SFENA HSI Power Up and ARINC 429 Test - Part 3

Not all HSIs have ADF data integrated right into the instrument. In most cases the HSI is paired up with RDDMI to give ADF/VOR and DME information. However, the SFENA HSI has pointers for two ADF channels which I think is a really neat feature of this particular instrument. The video below shows ARINC 429 words being sent on the slow 12Kb/sec bus with the ADF1 relative bearing data of 45º nose right:

The ARINC 429 labels used in the example above are:

• Label 162 - ADF Bearing Data (BNR)

L-1011 Avionics Bending: SFENA HSI Power Up and ARINC 429 Test - Part 2

The video clip in this posting shows the HSI displaying FMS data. The FMS data labels are transmitted as ARINC 429 words from the computer to the HSI. As in the previous post, the instrument is powered from a 115V 400Hz source. The labels transmitted for this example are both in BCD format as compared to the angular information transmitted yesterday, which was in BNR format. Below is an example for BCD encoded data in an ARINC 429 word for DME Distance.

The ARINC 429 labels used in this posting are:

• Label 001 - Distance to Go 
• Label 012 - Ground Speed (FMS)

The data sent from the computer to the instrument for the ARINC 429 Label 001 and 012 is refreshed every 200ms on a "slow" ARINC 429 bus. In ARINC 429 a 100Kb/sec bus is defined as "fast" and a 12KB/sec bus as slow. The SFENA HSI only uses one 100Kb/sec (fast) bus for Magnetic Heading, Drift and Ground Speed (IRS) and the rest of the labels are transmitted on a slow 12Kb/sec bus. Since the Ground Speed data shown in the example comes from the FMS and not the Inertial Reference System (IRS) the data is also transmitted on the slower FMS bus. 

L-1011 Avionics Bending: SFENA HSI Power Up and ARINC 429 Test - Part 1

Wow, it's been a long time that I have place a new posting into this blog. The last few months have been very busy and I have spend most of my time working on the MD-83 project with the National Museum of Commercial Aviation here in Atlanta. I also spent a week at the IEEE 31st DASC conference in Williamsburg, VA. So, I will use the start of the new month to get back into my regular blogging routine. The remainder of the year will bring a lot of avionics bending!

Over the last few days I have been working on power-up tests of the SFENA HSI that I have had in storage for quite some time. The instrument is completely ARINC 429 based and you might have seen some postings of the SFENA ADI that Javier Pérez-Mato has been able to power up and use for his paper on an Experimental Optical Wireless bus system.

The focus for the next few days and/or weeks will be the SFENA HSI and controlling all its functions via ARINC 429 driven out of XPlane. First, I have to make sure that the device actually powers up and that the majority of the mechanics are in good shape. The instrument takes 115V 400Hz input power at about 0.25A.

What you see in the clip above it he SFENA device first powering up from the power source and then receiving a number or ARINC 429 words. The test labels sent to the HSI are:

• Label 320 - Magnetic Heading 

 VOR Test (watch the VOR flag in the upper left hand side)

• Label 222 - Omnibearing 
• Label 100 - Selected Radial 

Course Test (rotating, with NAV flag visible in upper left hand side)

• Label 114 - FMS Course 
• Label 116 - Lateral Deviation or cross-track

The ARINC 429 messages are sent by a DDC-42924i5 card and the program driving it is written in C. As this gets more sophisticated I will post the C code or post a reference to it on GitHUB.

Avionics Bending: S.F.E.N.A. ADIs - Working

A few months ago I shipped a set of SFENA ADI's to an extremely talented student at the Universidad de Las Palmas de Gran Canaria (ULPGC). The Spanish Wizard, as I would like to title him now, Javier Pérez and his team got the SFENA ADIs to work by creating a very neat integration of the ARINC 429 protocol with X-Plane. Javier sent me the short youtube video link below. Amazing work! The ADIs will stay on loan with Javier for more time until he can do more work with them and also aid them in his research work. Once the ADIs return to Atlanta, they will become part of the L-1011 simulator exhibit at the National Museum of Commercial Aviation. 

Avionics Bending: SFENA ADIs are Going on a Trip

The SFENA ADIs are going on a trip to Spain for a few months. Javier Pérez at the Universidad de Las Palmas de Gran Canaria (ULPGC) will use the instruments in support of a paper that he will be writing over the next few months. The project will be heavily focused on driving the instruments with the ARINC 429 protocol. It will be really cool to see what Javier will be able to do with them. I will post some updates from time to time as he makes progress with the ADIs.

Avionics Bending: Attitude Director Indicator - ADI (Analysis and Pinout)

First power up of the two pilot side instruments. Without the ARINC 429 data the flags will not clear, however, the measurements on the power supplies show that they are intact. I am really curious to see if the instruments will work after being on the line for over 6800 hours, having been parked in the Arizona desert for 10+ years and being rough handled during de-install ... we will see over the next few weeks. The next step here will be to write the ARINC bridge between xPlane and the avionics buses.

So, just like the HSI from yesterday's post, the SFENA (Thales Group) ADI is a truly awesome instrument and shows some very clever mechanical engineering. Both the N32 and the N33 are very much a complete computer in a box that does both the ARINC 429 handling as well as all of the servo channel handling.

The main subsystems of the ADI are:

1. Input Processor
2. Central Processing Unit
3. A/D Converter
4. Attitude Servo Channels
5. Pointer and Command Bar Servomechanism
6. Failure Warning Indicators
7. Output Processor
8. Power Supply / Lighting

The ADI actually ingests fewer ARING 429 labels than the HSI does. The N33 HSI receives data on 8 ARINC buses, while the N32 ADI only receives data on 5 of the ARINC avionics buses. Here is a list of the buses and the respective ARINC lablels:

Bus 1 - FAST/SLOW (Label 142)
Bus 2 - Not used
Bus 3 - Localizer (Label 173), Glideslope (Label 174)
Bus 4 - Reciprocal ADI - Sin/Cos Recopy (Label 325), Sin/Cos Recopy (Label 324)
Bus 5 - Roll Angle (Label 325) and Pitch Angel (Label 324)
Bus 6 - Flight Director Commands - Roll Command (Label 141), Pitch Command (Label 140) and Yaw Command (Label 143)

All of the buses above run either at 12 Kb/s or 100 Kb/s ... Bus1 and Bus4 are 100 Kb/s buses.

Here is the pin-out for the SFENA N32 ADI J1 connector:

q	Remote Test	Switch Input
A	115V 400 Hz	Power
B	115V 400 Hz	Power
P	BUS 1	ARINC 429
R	BUS 1	ARINC 429
y	BUS 3	ARINC 429
w	BUS 3	ARINC 429
a	BUS 4	ARINC 429
b	BUS 4	ARINC 429
T	BUS 5 Primary	ARINC 429
U	BUS 5 Primary	ARINC 429
X	BUS 5 Alternate	ARINC 429
Y	BUS 5 Alternate	ARINC 429
V	Bus 5 Alternate and Primary Switch	Switch Input
K	BUS 6 - Flight Director Channel 1	ARINC 429
L	BUS 6 - Flight Director Channel 1	ARINC 429
G	BUS 6 - Flight Director Channel 2	ARINC 429
H	BUS 6 - Flight Director Channel 2	ARINC 429
FF	Pin Program CPT/FO	Logic
M	FD/A Flag	Logic
HH	F/S Flag	Logic
AA	G/S Flag	Logic
GG	LOC Flag	Logic
EE	FD Flag	Logic
z	Monitor Bus - Reciproacl ADI	ARINC 429
y	Monitor Bus - Reciproacl ADI	ARINC 429
e	Decision Height Warning Light
f	Decision Height Warning Light
D	Integral Ligthing	5V
E	Integral Ligthing	5V
g	Validity Output Glideslope
h	Validity Output Flight Director
m	Validity Output Fast/Slow

To see the ADI in check this blog posting: SFENA ADI Working with XPlane

Avionics Bending: Horizontal Situation Indicator - HSI (Analysis and Pinout)

Thanks to some very kind people at Thales (the company that acquired Sextant which acquired SFENA a long time ago) I have been able to do a lot more research around the SFENA ADIs and HSIs that I intend on using for the project.

The instruments I have are from the early 1980s. The design of the ADI and HSI is truly amazing and shows just how much attention to detail and quality went into the engineering of them. The ADI and the HSI are based on ARINC 429 which is by far the most common avionics bus standard in use today (however, it is slowly being replaced by more modern standards).

Both the SFENA N33 (HSI) and N32 (ADI) instruments are based on a rather simple 8bit microprocessor made by RCA … namely the 1802RCA. The instruments are actually somewhat multi-processor systems because they are split into an input processors, handling the ARINC 429 communications, and a central processor handling all of the data transformations and the servo motor control. In order to reduce space needed by the electronics and to reduce the need for expensive resources, many of the functions in the instruments are multiplexed and use the same subsystems.

Specifically on the HSI, there are a number of subsystems that make up the entire electronics complex:

1. Input Processors

2. Central Processing Unit

3. A/D Converter

4. Servo Channels and Controller

5. Pointer Servomechanism Channels

6. Flags and Annunciator Subsystem

7. Magnetic Wheel Drivers

8. Data Output Processor

9. Power Supply and Lighting

The data used by the HSI would have been produced by a number of systems on-board and delivered to the instrument of several ARINC 429 buses. To be exact, the instrument receives data from a total of 8 data buses.

Bus 1 – Primary Attitude and Heading Reference System (AHRS)

Bus 2 – Automatic Flight Control System (AFCS)

Bus 3 – Instrument Landing System (ILS)

Bus 4 – ADF 1

Bus 5 – Flight Management Computer or GPS

Bus 6 – ADF 2

Bus 7 – Reciprocal HSI

Bus 8 – VOR

The above listed buses all feed a number of ARINC 429 labels to the HSI. Here is a list of labels on each of the buses:

Bus 1 – Magnetic Heading (Label 320), Drift (Label 321) and Ground Speed (Label 012)

Bus 2 – Heading Select (Label 101)

Bus 3 – Localizer (Label 173), Glide Slope (Label 174) and QFU (Label 105)

Bus 4 – ADF 1 (Label 162)

Bus 5 – True Heading (Label 314), Drift (Label 321), NAV Course (Label 114), Cross Track Distance (Label 116), NAV Vertical Deviation (Label 117), Ground Speed (Label 012), Distance-To-Go (Label 001), Alert (Label 270) and TO-FROM (also Label 270 but different bit)

Bus 6 – ADF 2 (Label 162)

Bus 7 – MAG (sin, cos recopy) (Label 320) and TRU (sin, cos recopy) (Label 314)

Most of the busses above run ARINC 429 Low Speed (12Kb/s) … however Bus 1 and Bus 7 require the faster 100 Kb/s ARINC 429 bus speed. Besides the ARINC 429 data,. The instrument also has a number of logic inputs that control the flags and other elements. The discrete inputs are:

· Normal / Alernate Switching for AHRS ….. 0V Normal, 28V Alternate

· True-Mag Selection …. 0V MAG, 28V TRUE

· HDG Select/Drift Selection … 0V HDG SEL, 28V DRIFT

· Sensor Number …. 0V … 1, 28V … 2

· Mode Selection … has two ports (pins) to encode the mode

• 0V 0V ….. VOR
• 28V 0V …. ILS
• 28V 28V …. NAV/FMC
• 0V 28V …. NAV/GPS

· HDG SEL / Drift Flag …. 0V Normal, 28V Pointer to 180 degree

· Vertical Deviation Flag …. 0V Normal, 28V Flag Retracted

· Selection of Bus for Drift Angle …. 0V AHRS/IRS, 28V FMC/OMEGA

· Selection of Bus giving Ground Speed …. 0V AHRS, 28V FMC/OMEGA

Here is the J1 connector pin-out for the SFENA N33 HSI:

Pin	SFENA Description	Notes
A	115V 400HZ	POWER INPUT
B	115V 400HZ	POWER INPUT
T	AHRS IRS Normal	ARINC 429 Input
U	AHRS IRS Normal	ARINC 429 Input
X	AHRS IRS Alternate	ARINC 429 Input
Y	AHRS IRS Alternate	ARINC 429 Input
a	Reciprocal HSI	ARINC 429 Input
b	Reciproacl HSI	ARINC 429 Input
M	ILS	ARINC 429 Input
N	ILS	ARINC 429 Input
J	VOR	ARINC 429 Input
K	VOR	ARINC 429 Input
L	ILS/VOR	Switch Input
P	AFCS Controller	ARINC 429 Input
R	AFCS Controller	ARINC 429 Input
DD	True/Magnetic Heading Switch	Switch Input
G	FMC or OMEGA	ARINC 429 Input
H	FMC or OMEGA	ARINC 429 Input
EE	NAV Source Switching	Switch Input
t	ADF 1	ARINC 429 Input
u	ADF 1	ARINC 429 Input
V	ADF 2	ARINC 429 Input
W	ADF 2	ARINC 429 Input
BB	Vertical Deviation	Logic Signal
AA	Heading Select	Logic Signal
FF	Sensor Identifier	Logic Signal
m	Ground Speed Source	Logic Signal
k	Drift Source	Logic Signal
CC	HDG SEL/DRIFT	Logic Signal
z	Reciproacl HSI	ARINC 429 Output
y	Reciproacl HSI	ARINC 429 Output
D	5V Integral Lighting	POWER INPUT
E	5V Integral Lighting	POWER INPUT
g	Validity Output
n	Validity Output
f	Validity Output
p	Comparison Warning Output