SAE ARD 5708-2007 Frequently Asked Questions About IEEE-1394b and SAE AS5643《关于IEEE-1394b和SAE AS5643常见问答》.pdf
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1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2007 SAE International All rights reserved. No part of this publication m
3、ay be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA)
4、 Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org ARD5708 AEROSPACE RESOURCE DOCUMENT Issued 2007-03 Frequently Asked Questions About IEEE-1394b and SAE AS5643 RATIONALE This document is a compilation of frequently asked questions about the recently-published AS5643
5、 and AS5643/1 standards, both for the benefit of those currently implementing these standards and for those considering their use. Q1. Whats the difference between 1394a and 1394b? A1. IEEE-1394a-2000 and IEEE-1394b-2002 are both amendments to the original IEEE-1394-1995 standard. As per section 3.1
6、0.1 of IEEE-1394b-2002, “IEEE-1394a-2000 provides arbitration acceleration, improves the speed of bus resets, and adds suspend and resume power management capabilities to the bus.” Continuing on, later in this section, “IEEE-1394b-2002 supports the DS form of signaling used in IEEE-1394a-2000 and IE
7、EE-1394-1995 while adding a new form of signaling capable of much higher data rates between Beta ports.” This new form of signaling is a modified version of the 8b/10b coding scheme used for Fibrechannel and Gigabit Ethernet. It is DC-balanced, so it allows DC-free data transmission that is needed w
8、hen transformers or capacitors (to separate ground domains) are used in the signal path. The addition of a scrambler to all data and control signals results in a significant reduction (approximately 20 dB) in the radiated emissions when compared to earlier repetitive control patterns. Continuing on
9、in section 3.10.1 of IEEE-1394b-2002, “IEEE-1394b-2002 also supports new media, such as Category 5 (CAT-5) unshielded twisted pairs (UTPs), glass optical fiber (GOF), and plastic optical fiber (POF).” These new media allow maximum cable lengths greater than earlier limitations of 4.5 meters: 50 mete
10、rs for POF, 100 meters for GOF, and S100 operation over lengths of CAT-5 up to 100 meters. IEEE-1394a-2000 supports speeds of S100, S200, and S400. IEEE-1394b-2002 is backwards-compatible with IEEE-1394a-2000; in addition, IEEE-1394b-2002 extends bus speeds to S800 and S1600 and has architectural su
11、pport for S3200. Q2. Whats the difference between 1394b and the SAE implementation? A2. The SAE AS5643 base specification standardizes an approach for using IEEE-1394b-2002 in safety-critical/mission-critical applications for military and aerospace vehicles. It contains generic requirements that spe
12、cify data bus characteristics, data formats, and node operation. Additions include the use of asynchronous stream packets, a fixed frame rate synchronized with a STart Of Frame (STOF) packet, addition of a Vertical Parity Check, static assignment of channel numbers, pre-assignment of bandwidth, and
13、use of Anonymous Subscriber Messaging. The SAE implementation uses IEEE-1394b-2002-compatible devices. The AS5643/1 slash sheet establishes guidelines for the data bus cable and its interface electronics for a system utilizing S400 over copper medium over extended lengths. Whereas IEEE-1394b-2002 li
14、mits the distance between hops to be no more than 4.5 meters, the AS5643/1 slash sheet accommodates much longer distances (see cable selection guide contained in A7 below), and the hardware requirements and examples address many of the environmental conditions (electromagnetic compatibility, tempera
15、ture, vibration, etc.) that military and aerospace vehicles may experience. SAE ARD5708 - 2 - Q3. Where can I find enough information to understand 1394a and 1394b? A3. Start by obtaining the IEEE standards: IEEE-1394-1995, IEEE-1394a-2000, and IEEE-1394b-2002. “Firewire System Architecture”, by Don
16、 Anderson of Mindshare (), is the most well-known reference book on IEEE-1394; it explains aspects of the standard that may be ambiguous and supplies real-world technical examples, but it is no substitute for having the actual IEEE standards. The Texas Instruments website () is another good resource
17、 for IEEE-1394 application notes (http:/ revision 1.1 can be obtained here: http:/ Of course, the best way to learn more about the SAE 1394b standards is to get involved with the SAE AS1-A3 task group! Q5. What do you mean by “asynchronous streaming packets”? Are they asynchronous packets or are the
18、y streams? A5. Refer to section 6.2.3A of IEEE-1394a-2000 for a detailed write-up on asynchronous streams. An asynchronous stream packet is identical in format to that of an isochronous stream packet, except that it is transmitted during the asynchronous period, subject to the same arbitration requi
19、rements, including fairness, as other asynchronous request subactions. Asynchronous stream packets, like isochronous packets, use channel numbers for addressing whereas asynchronous request packets are mapped into 1394s 64 bit address space. Asynchronous stream packets do not require the allocation
20、of bandwidth, however allocation of channel numbers is required (may not be for AS5643), and may be easily filtered by hardware. Q6. In paragraph 3.1 of AS5643, it mentions that 1394 transmissions occur in a dual simplex manner on TPA and TPB. What does that mean? A6. Each port of an IEEE-1394b-2002
21、 physical device (PHY) contains the transmit differential signals (TPB) and the receive differential signals (TPA). As explained in paragraph 3.1 of AS5643, “packets can be transmitted on the TPB pair at the same time arbitration and or signaling is received on the TPA pair and packets can be receiv
22、ed on the TPA pair at the same time arbitration is transmitted on the TPB pair.” Q7. What is the maximum number of nodes, bus lengths, etc. on the bus? A7. Per IEEE-1394-1995 and IEEE-1394a-2000, the maximum number of nodes on a bus is 63. However, up to 1024 busses may be used with bridges connecti
23、ng them together. That provides for over 64,000 nodes in a system. Regarding cable length, IEEE-1394-1995, IEEE-1394a-2000 and IEEE-1394b-2002 define transmitter signaling, cable/connector loss, and receiver sensitivity. None of these specifications explicitly define a cable length, however with a w
24、orst case cable/connector the longest distance is 4.5 meters. The AS5643/1 slash sheet accommodates much longer distances adjusting a number of factors that affect maximum bus length, including bus speed, wire gauge and construction, termination methods, and the number of disconnects between hops; r
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