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Parameter: SELECTED HEADING
MSB = 90 degree
LSB = 0.0439450625 degree
octal label = 101
value = 150 degrees
28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11
1 1 0 1 0 1 0 1 0 1 0 1 × × × × × ×
In this example, MSB = 90° therefore the maximum value is 90×2 = 180°
MSB
SELECTED HEADING value
= 180×(1/2+1/4+1/16+1/64+1/256+1/1024+1/4096) = 150°
Parameter : MACH
MSB = 2.048 mach
LSB = 0.0000625 mach
octal label = 205
Value = 0.8325mach
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 × ×
We know that the MSB(=2.048) of the data field represents half the
maximum value, so the maximum value is 2.048×2=4.096
MACH value = 4.096×(1/8+1/16+1/64+1/8192)=0.8325 mach
(2) BCD word
The data field for BCD word consists of bit 11-29, the word is broken up
into five data groups with 4 bits in each group except the fifth (the most left)
group which only contains three bits. Each data group can contain the number 0
through 9 with the fifth group containing 0 through 7
32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
P SSM DATA FIELD SDI LABEL
BNR data word construction
32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
P SSM group 5 group 4 group 3 group 2 group 1 SDI LABEL
BCD data word construction
The BCD word is broken up into 5 data groups, meaning that the number of
significant bits is 5. The resolution and range are specified by ARINC.
Parameter: DME DISTANCE
octal label = 201
resolution : 0.01
value = 257.86 NM
29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11
(4 2 1) (8 4 2 1) (8 4 2 1) (8 4 2 1) (8 4 2 1)
0 1 0 0 1 0 1 0 1 1 1 1 0 0 0 0 1 1 0
2 5 7 8 6
Parameter : TRUE AIRSPEED
octal label = 230
resolution : 1
value = 565 knot
29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11
(4 2 1) (8 4 2 1) (8 4 2 1) (8 4 2 1) (8 4 2 1)
1 0 1 0 1 1 0 0 1 0 1 × × × × × × × ×
5 6 5 × ×
[8]The sign ( plus, minus, north, south, etc.) and the status of the transmitter
hardware are encoded in the bits that make up the sign and status matrix (SSM).
The SSM is made up of bits 29,30 and 31 for BNR words, and bits 30 and 31 for
BCD words.
BIT NO. DESIGNATION
31 30 BNR DATA
0
0
1
1
0
1
0
1
FAILURE WARNING
NO COMPUTED DATA
FUNCTIONAL TEST
NORMAL OPERATION
BIT NO.
29
DESIGNATION
BNR DATA
0 PLUS, NORTH, EAST, RIGHT, TO, ABOVE
1 MINUS, SOUTH ,WEST, LEFT, FROM, BELOW
BIT NO. DESIGNATION
31 30 BCD DATA
0
0
1
1
0
1
0
1
PLUS, NORTH, EAST, RIGHT , TO, ABOVE
NO COMPUTED DATA
FUNCTIONAL TEST
MINUS, SOUTH, WEST, LEFT, FROM, BELOW
[9] Bit 32 is the parity bit in the ARINC 429 data word .Bit 32 is set to "1" when
there are an even number of binary "1"s in the word and to a "0" when there
are an odd number of binary "1"s in the word .A parity bit 32 is transmitted as
part of each data word to permit simple error checks to be performed by the
ARINC receiver. These, together with data reasonableness checks also
performed by the receiver, may be used to prevent the display or other
utilizations of an erroneous or suspect word.
EXERCISE
A. Find out the explanations of the following words in your“English-Chinese
technical dictionary”
1. avionics [ P1-15 ]
2. BCD [ P1-20 ]
3. binary number system [ P1-20 ]
4. bit [ P1-20 ]
B. Translate the second paragraph of lesson 22 into Chinese
C. Explain the following abbreviations:
1. I/O
2. ARINC
3. DADC
4. BCD
5. SDI
6. SSM
7. MSB
D. Calculate yourself the decimal result by choosing a BNR word example
discussed in lesson 22.
E. Calculate yourself the decimal result by choosing a BCD word example
discussed in lesson 22.
LESSON 23
AIR TRAFFIC CONTROL
VOCABULARY
1. ATC= Air Traffic Control [ 'træfik] 空中交通管制
2. interrogate [ in'tergeit ] v. 询问
3. transponder [ træns'p nd ] n. 应答机
4. reply [ ri'plai ] n. ; v. 答复; 应答
5. locate [ lou'keit ] vt. 定位; 固定
6. pertinent data [ 'p:tinnt ] 相应的(有关的)数据(资料)
7. TCAS = Traffic Alert and Collision Avoidance system
['træfik]['l:t] [k'li n]['v idns]
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
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航空工程英语基础（中英文对照）(35)
