The RS-422 bus is used to communicate operator-entered data, CDU
messages, and CDU display data between the NAV computer and
the CDU,
and between the performance computer and the
CDU. Also, an RS-422
interface communicates Jeppesen data and flight plans between the
NAV computer and the database loader.
4. B.
(3) ARINC 429 Interface
ARINC 429 is a serial digital data bus standard used between
avionics system elements.
Data transmissions are open loop, i.e.,
sinks are not required to inform sources that information has been
received. Data is transmitted on a continuous basis from
the source
systems at rates sufficiently high to ensure small incremental value
changes between updates. The basic information element transmitted
is a digital word containing 32 bits. This data is sent in either
binary, binary coded decimal (BCD) or discrete formats. The least
significant bit and least significant character of each word are
transmitted first. Also, the least significant bit of the word is
the most significant bit of the label and the label is transmitted
ahead of the data in each case. The label is used to identify the
data within the word.
The bus transmits at either a 100-kHz (high
speed) rate or a 12.5-kHz (low speed) data rate.
The 429 serial bus is used to input the following data to the
navigation computer:
. VOR/ILS Radio Data
. DME Radio Data
● IRS Data
. OMEGA Data
. GPS Data
c AFIS Commands and Data
The navigation computer will output
sensor initialization data,
radio tuning commands, and various other required parameters to the
subsystems via two 429
buses (general bus No. 1 and No. 2). This
data is described in Table 206.
22-14-00
Page 298.157
Aug 15/91
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