1、 A DUAL SPEED, MIL-STD-1553B COMPATIBLE FIBER OPTIC DATA BUS M.S. Blaha. C.H. DeGennaro, S.F. Utley AT&T Bell Laboratories Whippany, New Jersey 07981 Abstract A demonstration system of a dual speed, fiber optic data bus is described. This work is based on a previously described concept (1) which env
2、isioned a data bus populated with MIL-STD-1553B avionic components which evolve as equipment is upgraded to higher data rates. The approach described herein provides for the coexistence of bus nodes operating at 1 Mb/s, and 20 Mb/s, on a single fiber bus medium. The 1 Mb/s interface of each node is
3、1553B compatible, making use of readily available hardware and software. Both existing, 1 Mb/s 1553B compatible interfaces and new equipment operating at 20 Mb/s have been shown to work simultaneously on the single bus structure. The design provides a sound, low-risk method for transitioning from cu
4、rrent 1Mb/s equipment to a unified bus structure incorporating both existing 1553B compatible components and newly designed higher speed equipment. Introduction The AT&T Fiber Optic 1553/MSDRT Data Bus provides an efficient means of improving the data handling capabilities of the 1553B data bus. Thr
5、ough the use of fiber optics and high speed digital multiplexing techniques, a single fiber optic bus can provide both 1 Mb/s and 20 Mb/s transmission capability when supported by 1553B bus hardware. The 20 Mb/s operation is based on the Multiple Speed Data Rate Transmission (MSDRT) concept, which i
6、nvolves multiplexing 20 Mb/s data with standard 1553B protocol in a manner which is invisible to 1 Mb/s users. This dual-speed capability provides retrofit high-speed capability to existing systems based on 1553B, and allows for graceful system growth in the event of system upgrades. A dual speed si
7、ngle fiber transmission bus was chosen over an approach using separate busses for 1 Mb/s transmission and for higher speed transmission because the single fiber bus approach is more reliable, less expensive, and lighter weight. The fiber optic bus is compatible with 1553B hardware, application and p
8、rotocol software, and error handling routines, resulting in reduced cost and schedule impact for future technology upgrades. In addition, the use of fiber optics offers inherent immunity to electro-magnetic interference, RF interference, electro-magnetic pulses, and is non-radiating. Approach The fi
9、ber optic data bus was designed to directly interface with existing 1553B bus controllers and remote terminal hardware. This was done to take advantage of existing technology and thereby reduce development time and cost. Operational control and error handling routines of the bus were accomplished by
10、 the 1553B application and protocol software. The bus is configured as a common point broadcast network capable of supporting up to 31 nodes. It is composed of Fiber Optic Interface Units (FOIUs), and an optical bus structure consisting of fiber optic cables, connectors, and dual-redundant passive s
11、tar couplers. The 20Mb/s operation is based on the MSDRT concept, which involves the multiplexing of 20Mb/s Manchester encoded data in place of 1553B data words. The 20Mb/s transfers are initiated whenever the bus controller requests a transfer from one 1553B user having high-speed add-on circuitry,
12、 to another similarly configured user. Figure 1 illustrates the format used in the demonstration system when inserting the 20Mb/s data into the 1Mb/s data bits. Figure 1. Message Containing High-Speed Data Figure 2 depicts the basic architecture of the 1553B MSDRT Data Bus. Each FOIU has an optical
13、output and optical input, which are connected via fiber to the star coupler. FOIU outputs are connected to inputs of the transmissive star coupler, and the optical signal is distributed to all of its outputs. Each of the star couplers outputs are subsequently connected by fiber back to the FOIUs inputs. This effectively forms an optical broadcast bus, which is identical in function to the 1553B bus it replaces. A transmissive star coupler provides a passive transmission path having an adequate optical loss characteristic and minimal impact on system optical dynamic range requirements.
