| 词条 | Gillham code | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 释义 |
|name=Gillham code |digits=12 |tracks=9..11[1][2] |digit_values= |weight= |continuity=no |cyclic=yes |minimum_distance=1 |maximum_distance=1 |redundancy= |lexicography=no |complement= }}Gillham code is a zero-padded 12-bit binary code using a parallel nine-[1] to eleven-wire interface,[2] the Gillham interface, that is used to transmit uncorrected barometric altitude between an encoding altimeter or analog air data computer and a digital transponder. It is a modified form of a Gray code and is sometimes referred to simply as a "Gray code" in avionics literature.[5] HistoryThe Gillham interface and code are an outgrowth of the 12-bit IFF Mark X system, which was introduced in the 1950s. The civil transponder interrogation modes A and C were defined in air traffic control (ATC) and secondary surveillance radar (SSR) in 1960. The exact origin of the term Gillham code is unclear, but by 1962 the code was broadly recognized under this name[6][7] and described in an FAA report.[8][9] By the mid-1960s the code was also known as MOA–Gillham code[10] or ICAO–Gillham code. ARINC 572 specified the code as well in 1968.[11][12] Once recommended by the ICAO for automatic height transmission for air traffic control purposes,[9] it is now discouraged[2] and has been mostly replaced by modern serial communication in newer aircraft. Altitude encoderAn altitude encoder takes the form of a small metal box containing a pressure sensor and signal conditioning electronics.[16][17] The pressure sensor is often heated, which requires a warm-up time during which height information is either unavailable or inaccurate. Older style units can have a warm-up time of up to 10 minutes; more modern units warm up in less than 2 minutes. Some of the very latest encoders incorporate unheated 'instant on' type sensors. During the warm-up of older style units the height information may gradually increase until it settles at its final value. This is not normally a problem as the power would typically be applied before the aircraft enters the runway and so it would be transmitting correct height information soon after take-off.[18] Light aircraft electrical systems are typically 14 V or 28 V. To allow seamless integration with either, the encoder uses a number of open-collector (open-drain) transistors to interface to the transponder. The height information is represented as 11 binary digits in a parallel form using 11 separate lines designated D2 D4 A1 A2 A4 B1 B2 B4 C1 C2 C4.[5] As a twelfth bit, the Gillham code contains a D1 bit but this is unused and consequently set to zero in practical applications. Different classes of altitude encoder do not use all of the available bits. All use the A, B and C bits; increasing altitude limits require more of the D bits. Up to and including 30700 ft does not require any of the D bits (9-wire interface[1]). This is suitable for most light general aviation aircraft. Up to and including 62700 ft requires D4 (10-wire interface[2]). Up to and including 126700 ft requires D4 and D2 (11-wire interface[2]). D1 is never used.[23][24]
DecodingBits D2 (msbit) through B4 (lsbit) encode the pressure altitude in 500 ft increments (above a base altitude of −1000±250 ft) in a standard 8-bit reflected binary code (Gray code).[23][26][27][28][29] The specification stops at code 1000000 (126500±250 ft), above which D1 would be needed as a most significant bit. Bits C1, C2 and C4 use a mirrored 5-state 3-bit Gray BCD code of a Giannini Datex code type[10][31] (with the first 5 states resembling O'Brien code type II[32][28][29]) to encode the offset from the 500 ft altitude in 100 ft increments.[5] Specifically, if the parity of the 500 ft code is even then codes 001, 011, 010, 110 and 100 encode −200, −100, 0, +100 and +200 ft relative to the 500 ft altitude. If the parity is odd, the assignments are reversed.[23][26] Codes 000, 101 and 111 are not used.[38]{{Rp|13(6.17–21)}} The Gillham code can be decoded using various methods. Standard techniques use hardware[38] or software solutions. The latter often uses a lookup table but an algorithmic approach can be taken.[26] See also
References1. ^1 2 3 {{cite web|title=Altitude - MODEC ASCII |author-first=Darryl |author-last=Phillips |date=2012-07-26 |orig-year=1998 |publisher=AirSport Avionics |url=http://www.airsport-corp.com/modecascii.txt |dead-url=yes |archive-url=https://web.archive.org/web/20120726003224/http://www.airsport-corp.com/modecascii.txt |archive-date=2012-07-26}} |chapter=Chapter 6. Displacement measurement |page=123 |url=https://books.google.com/books?id=8WEhBQAAQBAJ |quote=[…] Other forms of code are also well known. Among these are the Royal Radar Establishment code; The Excess Three decimal code; Gillham code which is recommended by ICAO for automatic height transmission for air traffic control purposes; the Petherick code, and the Leslie and Russell code of the National Engineering Laboratory. Each has its particular merits and they are offered as options by various encoder manufacturers. A discussion of their respective merits is outside the scope of this book. […]}}[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]2. ^1 {{cite web |title=Ameriking AK-350 Altitude Encoder |publisher=Ameri-king |url=http://www.ameri-king.com/altitude_encoder.html |access-date=2018-01-14 |orig-year=2004 |dead-url=yes |archive-url=https://web.archive.org/web/20160625175313/http://www.ameri-king.com/altitude_encoder.html |archive-date=2016-06-25}} 3. ^1 {{cite web |title=Model E-04 406/121.5 MHz ELT |work=Products |publisher=ACK Technologies, Inc. |date=2002 |url=http://www.ackavionics.com/products.htm |access-date=2018-01-14 |dead-url=no |archive-url=https://web.archive.org/web/20180116184013/http://www.ackavionics.com/products.htm |archive-date=2018-01-16}} 4. ^1 {{cite web |title=Altitude Encoder Model 8800-T Operating Manual |date=2016 |id=OP8800-TC Rev. F |publisher=Shadin Avionics |url=https://www.shadin.com/documents/manuals/OP8800TC.pdf |access-date=2018-01-14 |dead-url=no |archive-url=https://web.archive.org/web/20180116190458/https://www.shadin.com/documents/manuals/OP8800TC.pdf |archive-date=2018-01-16}} 5. ^1 2 3 {{cite web |title=Mode A and Mode C - The straight scoop on how it works |author-first=Darryl |author-last=Phillips |date=2012 |orig-year=1998 |publisher=AirSport Avionics |url=http://www.airsport-corp.com/modec.htm |access-date=2018-01-14 |dead-url=yes |archive-url=https://web.archive.org/web/20120614184629/http://www.airsport-corp.com/modec.htm |archive-date=2012-06-14}} 6. ^1 2 {{cite patent |title=United States Patent US3805041 - Circuit for converting one code into another code |inventor-first=Hans |inventor-last=Langheinrich |assignee=VDO Tachometer Werke Adolf Schindling GmbH |fdate=1971-10-27 |adate=1974-04-16 |id=Application 192830 patent 3805041 |url=http://www.freepatentsonline.com/3805041.pdf |access-date=2018-01-14}} 7. ^1 2 3 {{cite web |title=Aviation Gray Code: Gillham Code Explained |date=2010-12-03 |author-first=K. |author-last=Stewart |publisher=Custom Computer Services (CCS) |url=http://www.ccsinfo.com/forum/viewtopic.php?p=140960#140960 |access-date=2018-01-14 |dead-url=no |archive-url=https://web.archive.org/web/20180116184525/http://www.ccsinfo.com/forum/viewtopic.php?p=140960 |archive-date=2018-01-16}} 8. ^1 {{cite journal |title=(Unknown) |journal=computer design (cd) |publisher=Computer Design Publishing Corporation |date=1962 |volume=1-2 |page=45 |url=https://books.google.com/books?id=npg_AQAAIAAJ |access-date=2018-01-16 |quote=[…] Output code of a new Beacon encoder is known as the Gillham code, a modified Gray code designed to be compatible with both American and European traffic systems. […]}} 9. ^1 {{cite journal |title=(Unknown) |journal=Control Engineering |publisher=Technical Publishing Company |date=1963 |volume=10 |page=110 |url=https://books.google.com/books?id=DPpIAQAAIAAJ |access-date=2018-01-16 |quote=[…] Designed to be compatible with American and European traffic systems, a beacon encoder available from Norden Div., United Aircraft Corp., Nonvalk, Conn., puts out a modified Gray code known as the Gillham code. […]}} 10. ^1 {{cite book |title=Mark 2 Subsonic Air Data System |id=ARINC 572 |date=1968-02-15 |page=55 |publisher=Aeronautical Radio, Incorporated (ARINC) |location=Annapolis, Maryland, USA}} 11. ^1 {{cite book |title=Mark 2 Air Traffic Control Transponder |id=ARINC 572-1 |date= |page= |publisher=Aeronautical Radio, Incorporated (ARINC)}} 12. ^1 {{cite |author-first=Frank |author-last=Gray |author-link=Frank Gray (researcher) |title=Pulse code communication |date=1953-03-17}} (NB. {{US patent|2632058}} filed November 1947.) 13. ^1 2 {{cite book |title=Taschenbuch der Nachrichtenverarbeitung |language=German |editor-first=Karl W. |editor-last=Steinbuch |editor-link=Karl W. Steinbuch |date=1962 |edition=1 |publisher=Springer-Verlag OHG |location=Karlsruhe, Germany |publication-place=Berlin / Göttingen / New York |lccn=62-14511 |pages=71–74}} 14. ^1 2 {{cite book |title=Taschenbuch der Informatik – Band II – Struktur und Programmierung von EDV-Systemen |language=German |editor-first1=Karl W. |editor-last1=Steinbuch |editor-link1=Karl W. Steinbuch |editor-first2=Wolfgang |editor-last2=Weber |editor-first3=Traute |editor-last3=Heinemann |date=1974 |orig-year=1967 |edition=3 |volume=2 |work=Taschenbuch der Nachrichtenverarbeitung |publisher=Springer Verlag |location=Berlin, Germany |isbn=3-540-06241-6 |lccn=73-80607 |pages=98–100}} 15. ^1 {{cite journal |author-first=Joseph A. |author-last=O'Brien |title=Cyclic Decimal Codes for Analogue to Digital Converters |journal=Communication and Electronics |volume=75 |issue=2 |date=May 1956 |pages=120-122 |issn=0097-2452 |doi=10.1109/TCE.1956.6372498 |url=http://ieeexplore.ieee.org/document/6372498/?reload=true}} 16. ^1 {{cite book |title=(Unknown) |publisher=Federal Aviation Administration (FAA) |type=Report |date=May 1962}} 17. ^1 2 {{cite journal |title=(Unknown) |author=United Service and Royal Aero Club (Great Britain) |journal=Flight International |volume=85 |issue=2 |publisher=Illiffe Transport Publications |date=1964 |page=593 |url=https://books.google.com/books?id=v04eERVZ_HMC |quote=[…] Altitude encoding: A new […] encoder with an output in Gillham code, as recommended for altitude encoding by ICAO and described in an FAA report of May 1962, has been introduced […]}} 18. ^1 2 3 {{cite book |title=Honeywell System Installation Manual - Bendix/King KMH 880/KTA 870 Multi-Hazard Awareness Traffic Advisory System |id=Manual number 006-10609-0003 |edition=Revision 3 |date=August 2002 |orig-year=2001 |publisher=Honeywell International Inc. |url=https://petitcessnavoyageur.files.wordpress.com/2016/01/kmh880-kta-870-im-006-10609-0003_3.pdf |access-date=2018-01-18 |dead-url=no |archive-url=https://web.archive.org/web/20180118163000/https://petitcessnavoyageur.files.wordpress.com/2016/01/kmh880-kta-870-im-006-10609-0003_3.pdf |archive-date=2018-01-18}} 19. ^1 2 3 4 5 {{cite book |title=Aircraft Electrical and Electronic Systems - Principles, Operation and Maintenance |chapter=3.5.1 Gillham interface and Gillham code |author-first1=Mike |author-last1=Tooley |author-first2=David |author-last2=Wyatt |edition=1 |date=2009 |publisher=Butterworth-Heinemann (Elsevier Ltd.) |isbn=978-0-7506-8695-2 |page=69}} 20. ^1 2 {{cite web |title=US Patent: Analog to digital encoder |author-first=Edwin L. |author-last=Wheeler |publisher=Conrac Corp |date=1969-12-30 |orig-year=1968-04-05 |id=Patent US3487460A |url=https://encrypted.google.com/patents/US3487460 |access-date=2018-01-21 |dead-url=no |archive-url=https://web.archive.org/web/20180121204203/https://encrypted.google.com/patents/US3487460 |archive-date=2018-01-21 |quote=[…] The MOA-GILLHAM code is essentially the combination of the Gray code discussed thereinabove and the well known Datex code; the Datex code is disclosed in U.S. Patent 3,165,731. The arrangement is such that the Datex code defines the bits for the units count of the encoder and the Gray code defines the bits for each of the higher order decades, the tens, hundreds, etc […]}} 21. ^1 {{cite web |title=US Patent: Digital coding and translating system |author-first=Carl P. |author-last=Spaulding |publisher=Datex Corp |date=1965-01-12 |orig-year=1954-03-09 |id=Patent US3165731A |url=https://www.google.com/patents/US3165731 |access-date=2018-01-21 |dead-url=no |archive-url=https://web.archive.org/web/20180121204752/https://www.google.com/patents/US3165731 |archive-date=2018-01-21}} 22. ^1 {{cite web |title=Single Gillham code |author-first=Marc |author-last=D.F.S. |date=2000-11-27 |publisher=ForPilots |url=http://www.forpilots.com/archive/rec.aviation.owning/5/msg5377.htm |access-date=2018-01-17 |dead-url=no |archive-url=https://web.archive.org/web/20180117174656/http://www.forpilots.com/archive/rec.aviation.owning/5/msg5377.htm |archive-date=2018-01-17}} }} Further reading
2 : Data transmission|Avionics |
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