AR1

12 Channels, ARINC 429/575 Communications

The AR1 provides an ARINC 429/575 communications interface with 12 channels. This module only provides an interface and data management. Any specific protocol handling must be programmed by the user in the application layer. Each channel is programmable as either Tx or Rx.

ARINC 429 is a data transfer standard for aircraft avionics. It uses a self-clocking, self-synchronizing data bus protocol (Tx and Rx are on separate ports). The physical connection wires are twisted pairs carrying balanced differential signaling. Data words are 32-bits in length and most messages consist of a single data word. Messages are transmitted at either 12.5 or 100 kbit/s to other system elements that are monitoring the bus messages. The transmitter constantly transmits either 32-bit data words or the Null state. A single wire-pair is limited to one transmitter and no more than 20 receivers. The protocol allows for self-clocking at the receiver end, thus eliminating the need to transmit clocking data. ARINC 429 is an alternative to MIL-STD-1553.

ARINC 575 is an equipment characteristic for a Digital Air Data System (DADS) that provides essential air-data information for displays, autopilots, and other flight controls and instrumentation on commercial and transport-type aircraft. ARINC 575 defined a digital databus for distribution of information to displays and other systems. This databus was later described in ARINC 419 and became what is now known as ARINC 429. There are only minor differences between the digital databus of ARINC 575 and that of ARINC 429. The most significant difference is that ARINC 429 reserves bit 32 for parity, while ARINC 575 could use bit 32 for either parity (when BNR) or data (when BCD).

For both the ARINC 429 and ARINC 575 standards, each channel is software-selectable for transmit or receive, and for Hi or Lo speed. When receiving a message, the receiver logic converts the serial BRZ data stream to a 32-bit wide parallel data word. If the Label, SDI, and parity bits pass validation, the ARINC data word is sent to the Receive FIFO (to be read by the user). When transmitting a message, message data can be sent immediately or buffered for synchronized transmission. In buffer mode, ARINC words are read from the Txmit buffer and sent out at the Txmit Interval Rate. In repeat mode, ARINC message data is sent continuously. The user interface supports FIFO buffering and interrupts. Txmit data can be sent immediately or scheduled. To schedule a Txmit sequence, the Txmit FIFO can be loaded with a sequence of up to 256 ARINC data words. The transmission interval is programmable. Enabling the channel begins transmission. Tx and Rx data are continuously monitored and verified.

Features

• Receive/Transmit mode programmable per channel
• 100 kHz or 12.5 kHz operation per channel
• Transmit: 255 message FIFO or scheduled transmits per channel
• Async transmits during scheduled transmits
• Receive: 255 message FIFO or mailbox buffering per channel
• Message Validation (SDI/Label Filtering) on received messages per channel
• Selectable hardware parity generation/checking
• Receive time stamping
• Continuous BIT
• Loop-back test
• Tri-state outputs
• High and Low speed Slew Rate outputs