The 1394 cable standard defines three signaling rates: 98.304, 196.608, and 393.216 Mbps (megabits per second; MBps in this paper refers to megabytes per second.) These rates are rounded to 100, 200, and 400 Mbps, respectively, in this paper and are referred to in the 1394 standard as S100, S200 and S400. Consumer DV gear uses S100 speeds, but most 1394 PC adapter cards support the S200 rate. The signaling rate for the entire bus ordinarily is governed by the slowest active node; however, if a bus master (controller) implements a Topology_Map and a Speed_Map for specific node pairs, the bus can support multiple signaling speeds between individual pairs.
Each node usually have three connectors, although the standard provides for 1 to 27 connector per a devices physical layer or PHY. Up to 16 nodes can be daisy-chained through the connectors with standard cables up to 4.5 m in length for a total standard cable length of 72 m. 1394 truly qualifies as a plug-and-play bus.
Provided a major technical improvement, namely new port specification that provides 800 Mbit/s over the same 8P8C (Ethernet) connectors with Category 5e cable, which is specified in IEEE 802.3 clause 40 (gigabit Ethernet over copper twisted pair) along with a corresponding automatic negotiation that allows the same port to connect to either IEEE Std 1394 or IEEE 802.3 (Ethernet) devices.Though the potential for a combined Ethernet and FireWire 8P8C port is intriguing, as of November 2008, no products or chipsets include this capability
The IEEE 1394-1995 standard defines two bus categories: backplane and cable. The backplane bus is designed to supplement parallel bus structures by providing an alternate serial communication path between devices plugged into the backplane. The cable bus, is a non-cyclic network with finite branches, consisting of bus bridges and nodes (cable devices). Six-bit Node_IDs allow up to 63 nodes to be connected to a single bus bridge; 10 bit Bus_IDs accommodate up to 1,023 bridges in a system. This means, as an example, that the limit is 63 devices connected to a conventional 1394 adapter card in a PC.
The 1394 Trade Association announced that products would be available before the end of 2008 using the S1600 and S3200 modes that, for the most part, had already been defined in 1394b and were further clarified in IEEE Std. 1394-2008. The 1.572864 Gbit/s and 3.145728 Gbit/s devices use the same 9-conductor beta connectors as the existing FireWire 800 and are fully compatible with existing S400 and S800 devices. It competes with USB 3.0. S1600 (Symwave) and S3200 (Dap Technology) development units have been made, however because of FPGA technology DapTechnology targeted S1600 implementations first with S3200 not becoming commercially available until 2012.
Fig. 1. Topology of a typical PC-based 1394 bus system for DV applications.
The 1394 protocol is implemented by the three stacked layers shown in figure 2. The three layers perform the following functions:
The 1394 cable standard defines three signaling rates: 98.304, 196.608, and 393.216 Mbps (megabits per second; MBps in this paper refers to megabytes per second.) These rates are rounded to 100, 200, and 400 Mbps, respectively, in this paper and are referred to in the 1394 standard as S100, S200 and S400. Consumer DV gear uses S100 speeds, but most 1394 PC adapter cards support the S200 rate. The signaling rate for the entire bus ordinarily is governed by the slowest active node; however, if a bus master (controller) implements a Topology_Map and a Speed_Map for specific node pairs, the bus can support multiple signaling speeds between individual pairs. The 1394 Trade Association’s 1394.1 working group presently are refining and clarifying the setup requirements for handling interconnected devices with multiple signaling speeds.
You can obtain the final version of the IEEE 1394-1995 standard from the Institute of Electrical and Electronic Engineers, Inc., Customer Service, 445 Hoes Lane, P.O. Box 1331, Piscataway, NJ 08855-1331, voice (800)678-IEEE or (908)981-0060, fax (908)981-9667, e-mail [email protected] The USB 1.0 specification is available from http://www.usb.org/present.php. The Open Host Controller Interface (Open HCI) 1.0 specification, which applies to 1394 and USB hosts, is available from http://www.microsoft.com/hwdev/specs/busspecs.php. A wide variety of information on 1394-related products and activities is available from Adaptec Corp.’s site, http://www.adaptec.com, and on Texas Instrument’s IEEE-1394 Web pages, http://www.ti.com/sc/1394.
The IEEE’s Microcomputer Standards Committee commenced in 1986 a unification process for various serial bus implementations of the VME, Multibus II, and Future Bus standards. This effort resulted in the original development of what became the IEEE 1394-1995 standard in Fall 1995. 1394 is based on Apple Computer’s original 1394 bus, which was intended as a low-cost replacement for or supplement to the SCSI bus that is a standard feature of Macintosh and PowerMac computers. Apple and SGS Thomson, which has an UK patent applicable to 1394, license their patents “on reasonable and non-discriminatory terms to anyone wishing to obtain a license.” These licenses apply only to the point of first implementation, which means integrated circuits to implement 1394 connectivity, and thus are of no concern to most adapter card manufacturers or end users. Today’s licensees primarily are 1394 chip manufacturers, such as Texas Instruments, Adaptec and Symbios Logic, plus consumer electronics firms like Sony that incorporate some of the 1394 technology within their own specialized processor chips.
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