1、BRITISH STANDARD AEROSPACE SERIES BS G 264:2005 Specification for Avionic data transmission interface systems Utilities bus ICS 49.060 BS G 264:2005 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 15 March 2005 BSI 15 March 2005 The following
2、 BSI references relate to the work on this British Standard: Committee reference ACE/6 Draft for comment 02/696901 DC ISBN 0 580 45474 6 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee, ACE/6/9, Digital Data Buses, upon w
3、hich the following bodies were represented: British Airways ERA Technology Ltd. MOD UK Defence Standardization Society of British Aerospace Companies Ltd. Co-opted members Amendments issued since publication Date Amd. No. CommentsBS G 264:2005 BSI 15 March 2005 i Contents Page Committees responsible
4、 Inside front cover Foreword ii Introduction 1 1S c o p e 1 2 Normative references 1 3 Definitions 1 4 General requirements 3 5 Transmission method 4 6M e s s a g e f o r m a t s 6 7 Terminal operation 9 8 Bus characteristics 10 9 Terminal characteristics 15 Annex A (normative) Alternative bus 18 Bi
5、bliography 21 Figure 1 Simple utilities bus architecture 3 Figure 2 Bus encoding 4 Figure 3 Message format 5 Figure 4 Information transfer format 6 Figure 5 Synchronization and start bit patterns 6 Figure 6 Response time (polling cycle gap) 8 Figure 7 Message timings 9 Figure 8 Data bus interface us
6、ing transformer coupling 12 Figure 9 Coupling transformer 13 Figure 10 Bus interface using direct coupling 14 Figure 11 Terminal I/O Characteristics for transformer coupled stubs and direct coupled stubs 16BS G 264:2005 ii BSI 15 March 2005 Foreword This Standard defines a bit-serial dual redundant
7、utilities data bus operating at a signalling rate of 250 kbit/s for high integrity applications. It uses screened twisted pair data bus cable as the transmission medium, and employs transformer isolation at all terminals. For lower integrity applications an alternative (lower cost to connect) coupli
8、ng method is specified in Annex A. This Standard has been prepared by the UK Avionics Systems Standardisation Committee (ASSC) which is a joint Industry/MoD forum. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct applicati
9、on. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 21 and a back cover. The BSI copyright notice displayed in this document indicates when the docu
10、ment was last issued.BS G 264:2005 BSI 15 March 2005 1 Introduction Data bus technology provides an efficient means for the transfer of data between a number of processors, controls, displays, sensors, etc. within modern modular electronic systems. The first data bus standards to find general accept
11、ance in the aerospace industry were UK Def Stan 00-18 (Part 2) 1 /US MIL-STD-1553B 2 for military aircraft and ARINC 429 3 for civil aircraft. The data bus defined in this standard may be used in other military and commercial applications where high integrity operation is also required. With recent
12、developments in modular electronic systems there is a need for data bus technology to be applied to communications with low-level utility-functions (sensors, detectors, switches, indicators, relays and electrical-load controls, etc.) to achieve reliable operation in harsh environments such as aircra
13、ft. The bus system specified in this standard is designed to provide a high integrity, low cost, solution based on the proven technology of Def Stan 00-18 (Part 2)/MILSTD-1553B 12. It retains the same centralized control, command/response philosophy using transformer isolated terminals coupled to a
14、shielded, twisted pair, bus medium but operates at a lower 250 kbit/s with an increased addressing limit of 126 terminals. In practice the actual number of terminals and maximum data bus length used will be constrained by the electrical parameters of the implementation. 1 Scope This Standard specifi
15、es a high integrity, low cost to connect bit-serial dual redundant utilities bus operating at 250 kbit/s. The purpose of this document is to establish uniform requirements for data bus system techniques which will be used to control and monitor utilities based components and equipment. This utilitie
16、s data bus will enable the integration of, and promote standard system interfaces for, associated utilities sub-systems. This document also defines the concept of operation and information flow on the bus along with the electrical signalling and message formats to be employed. 2 Normative references
17、 The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Def Stan 00-18 (Part 2), Serial, Time Division,
18、Command/Response Multiplex Data Bus. RTCA DO-160/EUROCAE ED-14, Environmental Conditions and Test Procedures for Airborne Equipment. 3 Definitions For the purpose of this standard, the following definitions apply. 3.1 asynchronous operation use of an independent clock source in each terminal for mes
19、sage transmission. Decoding is achieved in receiving terminals using clock information derived from the message 3.2 Bi-phase space (Bi-S) an encoding scheme which has a level change at the beginning of every bit period which represents a zero by a mid-bit level change and which represents a one by n
20、o mid-bit level change 3.3 bit contraction of a binary digit (may be either zero or one). In information theory a binary digit is equal to one binary decision or the designation of one of two possible values, or states, used to store or convey informationBS G 264:2005 2 BSI 15 March 2005 3.4 bit rat
21、e the number of bits transmitted per second 3.5 broadcast operation of a data bus system such that information is transmitted by the bus controller or a remote terminal for reception by all terminals using the broadcast address 3.6 bus all the hardware including screened twisted pair cables, isolati
22、on resistors, transformers, etc., required to provide a single data path between the bus controller and all the associated remote terminals 3.7 Bus Controller (BC) the sole terminal that initiates all information transfers on the bus 3.8 Bus Monitor (BM) the terminal assigned the task of listening t
23、o bus traffic and extracting selected information to be used at a later time 3.9 command/response operation of a bus system such that remote terminals transmit only when commanded to do so by the bus controller 3.10 half duplex operation of a data transfer system in either direction over a single li
24、ne; but not in both directions on that line simultaneously 3.11 message the transmission of a sequence of: start, source identifier, address, data, parity, and stop bits 3.12 Non-Return to Zero (NRZ) a binary method of representation for Pulse Code Modulation (PCM) signals where one is represented b
25、y one level, and zero is defined as the other level in a bi-level system 3.13 Pulse Code Modulation (PCM) form of modulation in which the modulation signal is sampled, quantized, and coded so that each bit of information consists of different types or numbers of pulses and spaces 3.14 redundant bus
26、use of more than one bus to provide more than one data path between the subsystems, e.g. dual redundant bus, tri redundant bus, etc. 3.15 Remote Terminal (RT) any terminal not operating as the bus controller or bus monitor 3.16 Terminal hardware/software function which provides the interface between
27、 the bus and the host/user SubsystemBS G 264:2005 BSI 15 March 2005 3 3.17 Time Division Multiplexing (TDM) the transmission of information from several signal sources through one communication system with different signal samples staggered in time to form a composite pulse train. 4 General requirem
28、ents 4.1 Test and operating requirements NOTE All requirements specified herein should be met over the range of environmental conditions in which the utilities bus system is required to operate. 4.2 Bus operation The utilities bus system in its most elemental configuration is shown in Figure 1. The
29、utilities bus system shall function asynchronously in a command/response mode, and transmission shall occur in a half-duplex manner. Sole control of information transmission shall reside with the bus controller, which shall initiate all transmissions. 4.3 Data form Digital data may be transmitted in
30、 any format compatible with the data fields specified in Clause 6. Any unused bit positions shall be transmitted as logic zeros. 4.4 Bit priority The most significant bit shall be transmitted first, with the less significant bits following in descending order of value in the data word. Key 1 Bus A 2
31、 Bus B 3 Bus Controller 4 Remote Terminal 5 Remote Terminal Figure 1 Simple utilities bus architecture 1 2 345BS G 264:2005 4 BSI 15 March 2005 5 Transmission method 5.1 Modulation The signal shall be transferred over the bus in serial digital pulse code modulation form. 5.2 Data code The data shall
32、 be bi-phase space (Bi-S) encoded. A feature of this form of encoding is that the signal may be inverted without affecting data recovery. A transition shall be transmitted at the start of each data bit, and a logic zero bit shall have a transition at its midpoint (see Figure 2). 5.3 Transmission bit
33、 rate The transmission bit rate on the bus shall be 250 kbit/s with a combined accuracy and long term stability of 0.1%. Key A Clock B 1 bit time C NRZ DATA D Bi-s Data Figure 2 Bus encoding B A C D 101101 01101BS G 264:2005 BSI 15 March 2005 5 Key 1 Start (1 bit) 2 Source identifier (1 bit) 3 Addre
34、ss and source bit parity (1 bit) 4 Data parity (1 bit) 5 Data parity (1 bit) 6 Data parity (1 bit) 7 Stop (1 bit) Figure 3 Message format 1 MSB MSB MSB MSB 42 Sync (4-bits) Address (7-bits) Data (8-bits) Data (8-bits) Data (8-bits) 12 3 4 5 67BS G 264:2005 6 BSI 15 March 2005 6 Message formats 6.1 M
35、essage format 6.1.1 General The message format shall be as shown in Figure 3. The message size shall be 42 bits inclusive of the synchronization pattern, start, source identifier, address, data, parity and stop bits. The information transfer format shall be as shown in Figure 4. 6.1.2 Synchronizatio
36、n pattern The synchronization pattern shall comprise a string of four, encoded, logic one bits followed by a missing start-of-bit transition as shown in Figure 5. Figure 4 Information transfer formatKeyA SyncB StartC Rest of messageD Bus quiet stateE Bus quiet state Figure 5 Synchronization and star
37、t bit patterns * # # * Command Message from (BC “n“) Resonse Message from (RT “n“) Command Message from (BC “n+1“) Resonse Message from (RT “n+1“) Next Msg T1 T2 T1 T2 1 1111 1111 0 0 234564 2 N N N N N N AB C D EBS G 264:2005 BSI 15 March 2005 7 6.1.3 Start bit The start bit shall be a single logic
38、 zero bit to flag the start of a message, as shown in Figure 3 and Figure 5. 6.1.4 Source identifier This bit is used to identify the source of the message, with a 1 indicating a message from a BC (command), and a 0 indicating a message from an RT (response). 6.1.5 Address field The next seven bits
39、following the source identifier shall be the RT address. Each RT shall be assigned a unique address. Addresses in the range 0 to 126 decimal shall be valid RT addresses, with address 127 decimal reserved for the broadcast option. 6.1.6 Address and source identifier parity The next bit following the
40、address field shall be used for parity over the preceding 8 bits. Even parity shall be used. 6.1.7 Data fields The three data fields allow for the transmission of twenty-four data bits in a message. Unless otherwise specified by the system designer these bits shall be applied in accordance with 4.3
41、and 4.4. 6.1.8 Data parity The last bit in each data field shall be used for parity over the preceding 8 bits. Even parity shall be used. 6.1.9 Stop bit The stop bit shall be a single logic one bit. The message shall terminate with the end-of-bit transition as shown in Figure 6. 6.2 Message timing T
42、he timing between messages (commands from the BC and responses from the RTs) shall conform to Figure 6.BS G 264:2005 8 BSI 15 March 2005 6.3 Response time gap The RT shall respond, when it receives a valid command message for its address in accordance with 6.1, within the time period of 20 s to 350
43、s. This time period, shown as T1 in Figure 6 is measured at point A of the RT as shown in Figure 8 and Figure 10. The time is measured from the end of bit zero crossing transition of the stop bit (bit 42) of the command message, to the end of bit zero crossing of the first bit of the sync (bit 1) of
44、 the RT response. 6.4 Polling cycle gap The BC shall provide a minimum gap time of 20 s between the controller transmitting a broadcast command message or receiving a valid RT response message to the initiation of the next command message (see Figure 6). This time period, shown as T2 in Figure 6, is
45、 measured at point A of the RT as shown in Figure 8 and Figure 10. The time is measured from the end of bit zero crossing transition of the stop bit (bit 42) of the of the BC broadcast command message or RT response message, to the end of bit zero crossing of the first bit of the sync (bit 1) of the
46、 next command message. Key 1 BC Command message 2 RT Response or next BC broadcast command message 3 Bit 42 Stop bit 4 Bit 1 Sync 5 End of bit transition 6 See output symmetry requirement (9.1.1.5 and 9.3.1.5) T1 (T2) NOTE Waveforms may be inverted Response time gap, T 1(see 6.3) Polling cycle gap,
47、T 2(see 6.4) Figure 6 Response time (polling cycle gap) 1 2 34 5 6 T1 (T2)BS G 264:2005 BSI 15 March 2005 9 6.5 Minimum no-response timeout Following a non-broadcast command message the minimum time that the BC shall wait before instigating the next command message, when no valid response message fr
48、om the addressed RT has occurred, shall be 700 s. This time period, shown as T3 in Figure 7, is measured from the end of bit zero crossing of the first bit of the sync (bit 1) of the command message, to the end of bit zero crossing of the first bit of the sync (bit 1) of the next command message “n+
49、1”. 7 Terminal operation 7.1 Common operation 7.1.1 General Terminals shall have common operating capabilities as specified in 7.1.2 to 7.4. 7.1.2 Message validation Terminals shall check that each message received at a terminal conforms to the following minimum criteria: The message begins with a valid synchronization pattern. (see 6.1.2). The message has valid start and stop bits. (see 6.1.3 and 6.1.9) The four parity bits in t
