CHAPTER 3
Devices and Ports
USB Ports 29
Figure 3-1 USB Type A port and connector
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
1.5 Mbits per second and 12 Mbits per second, respectively. High-speed
operations requires the use of shielded cables.
Transfer Types Supported 3
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.
Table 3-1 Pin assignments on the USB port
Pin Signal name Description
1 VCC +5 VDC
2 D– Data –
3 D+ Data +
4 GND Ground
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