How Do Avionics Systems Communicate? New ARINC-429 Bus Board Announced by UEI
Learn about a new board that uses an FPGA for serial communication in avionics applications.
Learn about a new board that uses an FPGA for serial communication in avionics applications.
The DNx-429-516 ARINC-429 interface from United Electronic Industries (UEI) is designed for use with the company’s UEI’s Cube and RACKtangle chassis. It is compatible with ARINC-429 commercial aviation data standard.
This is an update to an earlier version, the DNx-429-516-024, and includes an additional 8 dedicated RX channels.
The DNx-429-516. Image from UEI
According to UEI's press release on the board, it "provides unprecedented flexibility to record, playback, process, and test... ARINC-429 traffic."
So, for those of us not in the aerospace industry, what is the ARINC-429 standard?
What Is ARINC-429?
ARINC-429 is the technical data transfer standard for avionics data bus employed by commercial aircraft. Within it are defined the physical and electrical standards for the two-wire twisted pairs that comprise the bus.
Messages are typically contained in one 32-bit long word, and transmission is at either 12.5 or 100 kilobits per second. The information is self-clocked, so no separate line is required for clocking.
ARINC standards are set by the Airlines Electronic Engineering Committee (AEEC). The military counterpart to ARINC-429 is Mil-Std-1553.
Specifications for the DNx-429-516
There are several channels on the DNx-429-516, including 16 TX/RX channels, which can be used on a channel-by-channel basis as RX channels by disabling the corresponding TX drivers. There are also 8 dedicated RX channels.
As seen in the block diagram below, the protocol controller uses a digital signal processing block with an FPGA, which has communication protocol functions embedded into it.
Block diagram for the DNx-429-516 TX single-channel. Image from the datasheet. Click to enlarge.
As ARINC-429 specifies, data transmission can be high speed (100 kHz), low speed (12.5 kHz), or other frequencies if need be on a channel-by-channel basis. The device manages ARINC-429 traffic while maintaining data integrity, "even when all channels are set in high-speed mode."
Transmission of all channels is scheduled by a hardware-controlled scheduler (with a transmission schedule resolution of 100 microseconds). Modes of transmission include a TX mode where a label is transmitted only upon receipt of data from a pre-programmed lab.
Alternatively, they can transmit asynchronously, with three priorities:
- High-priority data: Sent immediately, regardless of any scheduling constraints; will send upon completion of current transmission
- Standard-priority data: Sent during times when no scheduled data is being transmitted
- Low-priority data: Sent when no scheduled, high-, or standard-priority data is being transmitted; streamed from a 256-word FIFO
Documentation
The UEIDAQ Framework offers an API to access and control the DNx-429-516, as well as for other UEI data acquisition devices. UEI asserts that the API is easy to use and supports most popular operating systems and programming languages.
A user's manual for using the UEIDAQ framework API is available here. A user's manual for the DNx-429-516, itself, is available here.
Other Manufacturers
As might be expected for such an important application with an almost universal standard, there is much interest in ARINC-429 devices by a multitude of manufacturers. Here are two.
- North Atlantic Industries offers the AR429/575 module. This device provides up to six programmable ARINC-429 channels. Each channel is software selectable for transmit or receive, and for high or low speed. The unit is for either ARINC-429 or for the older ARINC-575 standard.
- Alta Data Technologies offers a wide range of ARINC-429 Interface boards. One specific item is the PMC-A429HD, which offers 16, 32 or 48 channels of RX and TX ARINC-429 channels.
Tell us about your experience designing with the ARINC-429 standard in the comments below.
