FireWire is a trademark of Apple Inc. and is used in accordance with the Apple Software License Agreement.
The FireWire standard is an interface technology for transferring data between devices and computers. It is a high-speed serial bus using differential signaling and runs at up to 400 Mbit/s. FireWire was designed by Apple Computer and Cypress Semiconductor.
It only includes one electrical interface, one physical connector type, and two data transfer rates. The two different data transfer rates are 500 megabits per second (Mbit/s) and 800 Mbit/s.
Some other manufacturers such as Intel also include the specification in their chipset-based products for their own proprietary use, but part of the specification is open and available to implementers.
Here is the answer for, which statement regarding the firewire standard is accurate?
The standard was originally intended only for the transfer of digital data over a single cable, but this limitation has been lifted and it now describes the format of cables (electrical and optical) and connectors (both male and female) necessary to connect devices.
The software library of the FireWire specification is called LibFireWire.
LibFireWire is available in source code form. It is available for all platforms that support FireWire, including Windows, Linux and Macintosh.
The latest software library (libFireWire v3) supports the IEEE 1394a and 1394b standards and provides a comprehensive set of APIs for writing applications to run under any operating system.
The transfer speed for FireWire is 400Mb/s in the default mode.
It is up to 800 Mb/s when in high-speed mode via a UHS-1 interface. The maximum theoretical data rate is 800 Mb/s when using a 4K shift clock frequency and 800 Mb/s by using a 4K shift clock combined with a 14-bit wide bus.
In practice, the transfer rate can be considerably lower since there are many other constraints on the speed of the interface, such as the bus bandwidth for data recovery from burst frames.
FireWire is capable of operating in either “hot plug” or “warm plug” modes.
The two modes are very similar, but differ in the amount of power supplied to the device when it is plugged into the bus.
Although all FireWire interfaces can provide power to devices, not all interfaces can operate in either hot plug mode.
The vast majority of FireWire implementations are designed to allow devices to be hot-plugged by default; however, this is not required by the specification.
FireWire uses a differential signaling scheme, with a very low skew.
It also provides a high bandwidth common mode data path to the host. This is different from USB since USB has a common mode pull-up resistor that grounds the data line to +5 volts.
Due to these attributes, FireWire can be used as a very rugged application interconnect with appropriate components. In addition, the ruggedness of the interface makes it suitable for use as an industrial connector interface where rugged conditions are normal or even expected.
It is referred to as the FireWire interface being “on” or being “enabled”.
This is part of the specification. The FireWire interface must be turned on before it can be used by compliant devices.
A device can query whether or not the bus is enabled by means of an inquiry command to determine if any other device controls the bus.
If all devices that respond to the inquiry are compliant with the FWspec, then no device controls (owns) the bus (and also controls) and may use it for data transfers.
Digital outputs are available to drive loads up to 100 W.
Digital output drivers are available to drive loads up to 100 W and power up to 2 A in the default mode and up to 4 A in high speed mode or when using a UHS-1 interface.
The maximum current provided by the output driver is limited by the current capability of the external power supply which must be capable of supplying at least 1.5 A in either case.
Consequently, if the highest power that may be connected is 100 W, then this limit applies when connecting an external power supply with an output current of 100 mA (i.e., 2×1.5=3 A).
Digital outputs may be used to control a fan motor or a relay.
There are two different types of digital outputs: those that can drive an active load and those that can drive a passive load.
A fan motor is controlled by supplying the signal to turn the motor on and off.
A relay uses power from the bus to operate an external circuit such as an electromagnet that closes a switch, which then completes the circuit.