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.