Full name IEEE 1394-1995. Also known as FireWire (Apple), iLink (Sony) or Lynx. Defines a serial data transfer protocol and interconnection system.
4 pin IEEE1394 FEMALE connector at the devices
|Firewire [IEEE-1394] defines a media, topology and protocol for both a backplane
physical layer or point-to-point serial cable interface. The interface is also
called the High Performance Serial Bus (HPSB). On the Apple computer it became
the high-performance replacement for the Apple Desktop Bus (ADB).
The backplane version uses two single ended signals and operates at 12.5 [TTL], 25 [TTL], or 50Mbits/sec [BTL or ECL].
The cable (differential) version operates at 100, 200, or 400Mbits/sec, [800Mbits/sec for 1394b] using half-duplex [full duplex 8B/10B encoding for 1394b].
Devices on the bus are Hot-Swappable. It supports up to 63 devices at a maximum cable distance between devices of 4.5 meters. The maximum devices on the bus is 16 allowing a total maximum cable distance of 72 meters. Transmitting data over CAT5 cable allows data at 100Mbps to travel 100m [1394b]. Fiber cable will allow 100 meter distances at any speed [depends on the type of fiber cable].
The digital interface supports either asynchronous and isochronous data transfers. Addressing is used to a particular device on the bus. Each device determines its own address.
The IEEE 1394-1995 standard for the High Performance Serial Bus, here abbreviated to 1394, defines a serial data transfer protocol and interconnection system that "provides the same services as modern IEEE-standard parallel busses, but at a much lower cost." 1394 incorporates quite advanced technology, but it"s the "much lower cost" feature that assures 1394"s adoption for the digital video and audio consumer markets of 1997 and beyond. The capabilities of the 1394 bus are sufficient to support a variety of high-end digital audio/video applications, such as consumer audio/video device control and signal routing, home networking, nonlinear DV editing, and 32-channel (or more) digital audio mixing. Sony"s DCR-VX700 and DCR-VX1000 digital video (DV, formerly called DVC) camcorders, introduced in September 1995, were the first commercial products to implement 1394. Subsequently Sony introduced in late 1996 its DCR-PC7 micro-DV camcorder and Matsushita announced in early 1997 Japanese availability of the Panasonic NV-DE3 DV camcorder with a 1394 connector.IEEE - 1394 Features
This objective of this paper is to describe the architecture of 1394 bus systems, typical consumer video and audio applications for 1394, initial implementations of 1394 connectivity on PCI adapter cards, and the commercial adapter card designs that are scheduled for availability by mid-1997 for digital video editing applications. A brief comparison of the IEEE 1394 High Performance Serial Bus with the proposed Universal Serial Bus (USB) appears at the end of this paper. The orientation of this paper is toward consumer- and professional-grade DV products, because DV is the first application (and is likely to be the highest-volume application through 1998) for the High Performance Serial Bus.
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.
IEEE - 1394 Architecture
The 1394 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, which is the subject of this paper, is a "non-cyclic network with finite branches," consisting of bus bridges and nodes (cable devices). Non-cyclic meansthat you can"t plug devices together so as to create loops. 16-bit addressing provide for up to 64K nodes in a system. Up to 16 cable hops are allowed between nodes, thus the term finite branches. A bus bridge serves to connect busses of similar or different types; a 1394-to-PCI interface within a PC constitutes a bus bridge, which ordinarily serves as the root device and provides bus master (controller) capability. A bus bridge also would be used to interconnect a 1394 cable and a 1394 backplane bus. 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.
Each node usually has three connectors, although the standard provides for 1 to 27 connector per a device"s 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. (Using higher-quality "fatter" cables permits longer interconnections.) Additional devices can be connected in a leaf-node configuration, as shown in figure 1. All 1394 consumer electronic devices announced as of early 1997 have only a single connector; there are no currently are digital camcorders or VCRs that correspond to the devices with ID 3 or ID 5 shown in figure 1. Physical addresses are assigned on bridge power up (bus reset) and whenever a node is added or removed from the system, either by physical connection/disconnection or power up/down. No device ID switches are required and hot plugging of nodes is supported. Thus 1394 truly qualifies as a plug-and-play bus.
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.
Physical, Link, and Transaction Layers
The 1394 protocol is implemented by the three stacked layers shown in figure 2. The three layers perform the following functions:
Cables and Connectors
Standard bus interconnections are made with a 6-conductor cable containing two separately-shielded twisted pair transmission lines for signaling, two power conductors, and an overall shield (see figure 3). The two twisted pairs are crossed in each cable assembly to create a transmit-receive connection. The power conductors (8 to 40 v, 1.5 a max.) supply power to the physical layer in isolated devices. Transformer or capacitative coupling is used to provide galvanic isolation; transformer coupling provides 500 volts and lower-cost capacitative coupling offers 60 volts of ground potential difference isolation. Connectors are derived from the GameBoy design and use either a friction detent (standard) or the special side-locking tab restraints shown in figure 3.* (You squeeze the sides of the connectors for removal.) 1394 connectors are available from Molex and several other firms.
1394 provides a flexible bus management system that provides connectivity between a wide range of devices, which need not include a PC or other bus controller. Bus management involves the following three services:
On bus reset, the structure of the bus is determined, node IDs (physical addresses) are assigned to each node, and arbitration for cycle master, isochronous resource manager, and bus master nodes occurs. Figure 4 illustrates on a timeline the identification and arbitration processes that occur on bus reset. Note that during the 1-second delay isochronous resources that had been allocated before the reset are to be reallocated. Any resources that are not reclaimed will become available for future use. After that delay new resources may be allocated.
Isochronous Data Transport
The isochronous data transport of the 1394 bus provides the guaranteed bandwidth and latency required for high-speed data transfer over multiple channels. The isochronous resource manager includes a BANDWIDTH_AVAILABLE register that specifies the remaining bandwidth available to all nodes with isochronous capability. On bus reset or when an isochronous node is added to the bus, the node requests a bandwidth allocation. As an example, a DV device would request approximately 30 Mbps of bandwidth, representing the 25+ Mbps DV data rate plus 3-4 Mbps for digital audio, time code, and packet overhead. Bandwidth is measured in bandwidth allocation units, 6,144 in a 125 ms cycle. (A unit is about 20 ns, the time required to send one data quadlet at 1,600 Mbps, called the S1600 data rate; the S1600 data rate is unlikely be supported in future implementations. A quadlet is a 32-bit word; all bus data is transmitted in quadlets.) 25 ms of the cycle is reserved for asynchronous traffic on the bus, so the default value of the BANDWIDTH_AVAILABLE register on bus reset is 4915 units. In a 100-Mbps system, a DV device would request about 1,800 units; in a 200-Mbps system, about 900 units would be sufficient. If adequate bandwidth is not available, the requesting device is expected to repeat its request periodically.
The isochronous resource manager assigns a channel number (0 to 63) to nodes that request isochronous bandwidth based on values in the manager"s CHANNELS_AVAILABLE register. All isochronous packets are identified by the assigned channel number. When a node no longer requires isochronous resources, it is expected to release its bandwidth and channel number. As an example, the bus manager sends signals to cause a camcorder to commence talking on its channel and a record deck to commence listening on its channel for video data from the bus manager application. Device control is managed by asynchronous communication. Video acquisition for non-linear digital editing is simpler than the camcorder-DVCR example, because it requires only a single isochronous channel, plus an asynchronous path for device control. Timecode is built into the DV data, but asynchronous timecode transmission over the bus is useful when in camcorder or DVCR shuttle mode.
Consumer Electronics Applications for 1394
The majority of the informative illustrations in the 1394 standard show interconnections between consumer video devices, with and without attached PCs. Based on the draft standard, 1394 Trade Association documents, and conversations with members of the Association, following are the primary consumer electronics applications anticipated for the High Performance Serial Bus. The products are listed in the author"s forecast order of their introduction to the retail market.
A principal advantage of the use of 1394 to interconnect DV and digital audio (DA) gear is that the 1394 bus is operable without a bus manager, and any "talker" device can arbitrate for assignment as the isochronous resource manager. Thus a DV camcorder, simple DVCR, printer, and DTV set can be connected without the need for a PC or other device to act as a bus manager. Assuming the camcorder is the "talker" and all other devices are "listeners," only a single, fixed isochronous channel is required. The camcorder starts talking in response to a local or remote control device, and the other DV devices listen or not, depending on their control status. One also could create a low-end equivalent of the $60,000+ Avid/Ikegami fixed-disk camcorder (CamCutter) with a battery-powered 1394 fixed or removable disk drive in a belt-pack, assuming the disk drive has enough built-in "smarts" to handle disk I/O chores and generate unique file names for successively-recorded bitstreams. Such a device would eliminate the need to copy video and audio data from tape to disk in the editing studio, the original objective of the CamCutter. High-capacity fixed disk drives are required; DV content at 3.5 MBps fills 1G in less than 5 minutes.
6 pin IEEE1394 FEMALE connector at the devices