Gables ATC Head: ARINC 429 Receive Tests

Taking a short break from the SFENA HSI today and tested ARINC 429 receive words with the DDC card. So far all the stuff you saw with the SFENA HSI had been ARINC 429 transmit words. The receive mode used in this example is called "mailbox" mode in which the channel on the card only remembers the last word received for a specific label. I had a Skype discussion with Edo from Italy today who is building a B767 simulator and we talked about the difference of using 2-of-5 and ARINC 429 label encoding. In 2-of-5, which is typical for ARINC 500 class devices, an ATC code or a radio frequency would be sent over 18 ore more discrete pins. Here is an example of how 2-of-5 encodes individual digits on individual pins:

2 of 5 Code used in ARINC 500 Series

The ARNC word still encodes the individual digits, but, does so in BCD format. The ARINC 429 Label also has some status information as part of a 32bit word that is being transmitted. All this data is transmitted on just two pins.

ARINC 429 Word for ATC Transponder

Typically BCD encoding uses 4 bits, however, since each position in the Transponder code only goes from 0 to 7 each digit can be encoded in 3 bits only. The video below shows a short introduction to reading the ARINC 429 label as shown above and doing a simple dump to the screen. The code is written in C.