Hi there.....I try to add more of my previous collegue
An ARINC 429 data bus uses two signal wires to transmit 32 bit words.
Transmission of sequential words is separated by at least 4 bit times of
NULL (zero voltage). This eliminates the need for a separate clock signal
wire. Thats why this signal is known as a self-clocking signal.
The nominal transmission voltage is 10 ±1 volts between wires (differential), with either a positive or negative polarity.
Therefore, each signal leg ranges between +5V and -5V. If one leg is +5V, the other is -5V and vice versa. One wire is called the A (or + or HI) side and the other is the B (or - or LO) side.
This is known as bipolar return-to zero (BPRZ) modulation.
The composite signal state may be one of three levels:
-
HI which should measure between 7.25 and 11 volts between the two
wires (A to B)
-
NULL which should be between 0.5 and -0.5 (A to B).
This is an old but common standard in avionic comm, now is overcoming the Arinc629 with optic fiber so.......better tecnology surely but completely another story!
Bye bye....
- LO which should be between -7.25 and -11 volts (A to B)