ARINC 429, "Mark 33 Digital Information Transfer System (DITS)," is a technical specification for an avionics data bus used on most high-end commercial and transport aircrafts.

At the physical layer, it features communication of data words over unidirectional, two-wire, bipolar electrical interface. Bit-encoding and decoding is controlled by a self clocking RZ signal and self-synchronizing data bus protocol. The transmit and receive channels are on separate ports.

In transmit, a single wire pair has one transmitter and supports up to 20 receivers. ARINC 429 data words are 32 bits (sometimes 25 bits), and most messages consist of a single data word. Messages are transmitted at either low speed (12.5 kbit/s) or high speed (100 kbit/s) to receiver elements. The transmitter constantly transmits either 32-bit data words or the NULL state.