曝光台 注意防骗
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67. denote [ di'nout ] vt. 指的是;意味着;指明
68. break up 分开
69. except [ ik'sept ] prep. 除…之外
70. resolution [ rez'lju:n ] n. 分辩率
71. hardware [ 'ha:dw ] n. 设备;金属构件;硬件
72. even [ 'i:vn ] a. 偶(数的)
73. odd [ d ] a. 奇(数的)
74. permit [ p'mit ] v. 允许
75. reasonableness [ ri:znblnis ] n. 合理性
76. utilization [ ju:tilai'zein ] n. 应用; 利用
77. erroneous [i'rounjs ] a. 错误的
78. suspect [ ss'pekt ] a. 可疑的
TEXT
[1] The commercial airplanes introduced during the 1980s such as A310,
B757/737, incorporate approximately 110 digital data buses, handling over one
thousand different parameters. If analog transmission techniques were used
exclusively, a bus and bus I/O circuit would be required for each parameter. The
increasing use of state-of-the-art digital techniques in avionics equipment and
need to reduce airplane wiring prompt development of the airplane-wide
digital bus system .
[2] Aeronautical radio incorporated company (ARINC) is a corporation made up
of scheduled airlines, transport companies, aircraft manufacturers and some
foreign airlines, the primary activity of ARINC is to produce specifications.
There are many ARINC specifications in existence, ARINC 453 is the
specification for very high speed digital transfer system. ARINC 573 is the
specification for digital flight data recording systems, ARINC 561 is the
specification for inertial navigation system, ARINC 708 is the specification for
airborne weather radar etc. ARINC 429 specification defines the standards for
transfer of digital data between avionics systems elements. This specification
describes a method of transmitting information from a designated output port of
a LRU to other systems requiring the information.
[3] Each LRU may have as many transmitters and receivers as required by the
overall airplane systems. For example, DADC supplies digital information to 3
different using systems on one bus while the DADC may output other
information to other systems from a second transmitter in DADC. If a system
requires input data from an additional data source, the system must have a
second receiver wired to the transmitted port of the other source. Each twisted
wire pair is a unidirectional bus. Bi-directional data transmission between two
LRUs must be accomplished by two twisted wire pair buses .
[4] Three most common types of ARINC 429 data word are: Binary coded
Decimal (BCD),Binary (BNR), and discrete. The format for BCD and BNR
words is similar. Each data word contains 5 parts, they are word label,
source/destination identifier (SDI), data field, sign/status matrix (SSM) and
parity bit (P). A discrete word contains a word label, parity bit and discrete
information. The ARINC 429 data words are transmitted at 12.5KHz (low speed)
or 100KHz (high speed).
[5] Each data word consists of 32 bits. The first 8 bits are called the octal label
which identifies the type of information contained within the word. For example,
true airspeed has an octal label of 230, true airspeed will always have an octal
label of 230 regardless of where the information originates.
[6] The source/destination identifier (SDI) may be used to identify the source of
a word. When words with the same label are sent from two or more installations,
the source of each word is identified by the SDI. When a word needs to be
directed to one of several installations, the destination of the word is identified
by the SDI, bit 9 and bit 10 represent SDI.
[7] Data is encoded in the data field. When all available bits in the data field are
not used they are filled with pad bits which are logic O's and have no
significance in the data transmitted .
(1) BNR word
The data field for a binary word consists of bit 11～28, bit 28 is the most
significant bit (MSB). The MSB of the data field represents half the maximum
value of the defined parameter. Following the MSB, each bit represents the
increments of a binary fraction series. The first bit to the left of the pad bits is
the
28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11
0 0 1 1 0 1 0 0 0 0 0 0 1 0 0 0 × ×
1/2 1/4 1/8 1/16 1/32 1/64 1/128 1/256 1/512 1/1024 1/2048 1/4096 1/8192 1/16384 1/32768 1/65536 1/131072 1/262144
Least Significant Bit (LSB). The word value is obtained by converting the
binary number to decimal.
In the following examples, the octal label is given along with the parameter
name. The value of the parameter, value of the MSB and value of the LSB are
given. X denotes padded to zero and not part of the word.
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