This section defines the Plug and Play requirements for IEEE 1394 cabling and connectors.
23. Device provides three connector ports
Recommended
All devices should provide three 6-pin connector ports for optimum cabling options, subject to cable-power distribution constraints. Fewer than three ports promotes long daisy chains, increasing the potential for speed traps (a slow device separating two faster devices). Therefore, three-port IEEE 1394 device nodes are recommended, with exceptions noted in the “Device uses standard 6-pin IEEE-1394 connector” requirement later in this section.
For internal-only devices, a minimum of two ports enables daisy chaining of devices. However, a limit of 15 hops (end-to-end distance) restricts total devices to 16, sufficient for most internal configurations.
Devices that consume cable power should be limited to a single connector to encourage short source-to-sink power delivery while eliminating the build up of voltage drop associated with a long daisy chain of power consumers.
24. Device uses standard 6-pin IEEE 1394 connector
Required
A single connector eliminates unnecessary choices for the end user. For every n supported connector, there are 2n – 1 cable choices. Two connector styles yield three end-user cable choices. Consistent use of the standard 6-pin IEEE 1394 connector eliminates an undesirable break in the power bus for power-dependent device applications.
Other benefits include volume pricing and consistent electrical performance. Therefore, all external pluggable IEEE 1394 devices must use the standard 6-pin IEEE 1394 connector. The exception is an option to use the 4-pin IEEE 1394A connector for miniature single-port (leaf-node) devices, as defined in the “Only single-port leaf-node devices use 4-pin connectors” requirement later in this section.
25. Self-powered devices propagate the power bus through each connector
Required
Self-powered devices provide their own power source and do not consume cable power. The exception to this rule is that a self-powered device can consume cable power up to the number of watts defined in 1394 Specification for Power Management in order to power its own PHY if it is not able to continue to power its own PHY when the self-powered device has been turned off.
If the self-powered device does consume cable power to power its own PHY, it must always use cable power to do so whenever cable power is present. That is, it cannot dynamically switch between consuming and not consuming cable power for PHY power.
Self-powered devices that provide their own power source and do not consume cable power must maintain the electrical integrity of the power bus for other devices dependent on it. Therefore, all self-powered IEEE 1394 devices must propagate the power bus through each connector. To accomplish this, each self-powered device must short together the power pins and the ground pins of each connector.
26. Only single-port leaf-node devices use 4-pin connectors
Required
The 4-pin connector offers a slightly lower cost and a smaller footprint ideally suited to hand-held devices. Use of a unique leaf-node connector adds one more cable choice for end users. Therefore, devices can comply with this specification by restricting application of the 4-pin (powerless) A/V connector to single-connector leaf-node devices. The 4-pin connector is specified in the IEEE 1394A specification.
27. Device connectors exhibit common speed and power characteristics
Required
Devices with multiple connectors must exhibit common characteristics at each connector to reduce end-user cabling choices. All connectors on a device must exhibit homogeneous speed, power, and mechanical characteristics such that:
Optionally, all devices providing cable power through 6-pin connectors must provide diode isolation as specified in the 1394 Trade Association Power Specification Part 1: Cable Power Distribution.
28. Standard 400-Mb/s rated IEEE 1394 cable provided with devices
| Required |
For Plug and Play, it is important to use one standard-performance cable for all device configurations to eliminate cable choices for the end user. This is especially important given the range of devices possible on an IEEE 1394 bus. A mix of cable types and ratings creates an unfriendly user experience. Therefore, all cables must be have a minimum 400-Mb/s rating and, if bundled, must be shipped with a standard cable.