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USB Ports

The Power Mac G5 computer has two external Universal Serial Bus (USB) 2.0 ports on the back and one on the front of the enclosure and an internal connection to the AGP slot for the Apple display. The external USB ports are off of the USB controller connected to the PCI bus, bridged by K2. In addition, there are two USB 1.1 ports on the keyboard. The USB ports are used for connecting the keyboard and mouse as well as additional I/O devices such as printers, scanners, and storage devices.

All USB ports are fully compliant with the USB 2.0 specification, including support for high-speed (480 Mbps) devices using an Enhanced Host Controller Interface (EHCI). Ports are automatically routed to a companion OHCI controller when a classic-speed (full-speed or low-speed) USB device is attached to a root hub port.

Each USB rear port is connected to a separate USB root hub in classic speeds, allowing the USB ports to support 12 Mbps devices at the same time with no degradation of their performance. The USB root hubs are also connected to the internal USB modem.

The three external USB ports comply with the Universal Serial Bus Specification 2.0. The two ports on the keyboard comply with the Universal Serial Bus Specification 1.1 Final Draft Revision. For low-speed and full-speed devices, the USB register set complies with the Open Host Controller Interface (OHCI) specification. For high-speed devices, the USB register set complies with the Enhanced Host Controller Interface (EHCI) specification.

For more information about USB on Macintosh computers, please refer to Apple Computer’s Accessing Hardware from Applications and the other sources listed in “USB Interface.”

In this section:

USB Connectors
Waking Up From Sleep

USB Connectors

The USB ports use USB Type A connectors, which have four pins each. Two of the pins are used for power and two for data. “Figure 3-1” shows the connector and “Table 3-1” shows the signals and pin assignments.

The Power Mac G5 computer provides 5 V power for the USB ports and up to 500 mA on each port. The power is provided in both run and sleep mode. The ports share the same power supply; a short circuit on one disables all ports until the short has been removed.

The USB ports support all USB 2.0 speeds: high-speed (480 Mbps) and classic USB speeds of full-speed (12 Mbps) and low-speed (1.5 Mbps). High-speed operation requires the use of shielded cables.

The Macintosh system software supports all four data transfer types defined in the USB specification, as well as split transactions for classic-speed devices attached to high-speed hubs.

Waking Up From Sleep

As defined in the USB-suspend mode of the USB specification, USB devices can provide a remote wakeup function for the computer (resume signalling). The USB root hub in the computer is set to support remote wakeup whenever a device is attached to the bus. The device wakes the computer by sending a RESUME event to the USB root hub. The mouse and keyboard that come with the computer use this method to wake the computer on a key press or mouse click.

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