Apple Desktop Computer manual Transfer Types Supported, Gnd

C H A P T E R 3

Devices and Ports

Figure 3-1USB Type A port and connector

Table 3-1Pin assignments on the USB port

Pin	Signal name	Description
1	VCC	+5 VDC
2	D–	Data –
3	D+	Data +
4	GND	Ground

The iMac computer provides 5-volt power at 500 mA for each of the two ports.

The USB ports support both low-speed and high-speed data transfers, at up to

1.5Mbits per second and 12 Mbits per second, respectively. High-speed operations requires the use of shielded cables.

Transfer Types Supported

The USB specification defines four data transfer types:

■Control transfers, used for device configuration and initialization.

■Bulk transfers, used for printers, scanners, modems, and other devices that require accurate delivery of data with relaxed timing constraints.

USB Ports 29