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Universal Serial Bus (USB) Ports
The Universal Serial Bus connects USB devices with a USB host, in this case, the Little Board/P5
x
.
The USB physical interconnect is a tiered star topology, or tree, consisting of hubs and USB
devices. Each USB segment is a point-to-point connection between hubs or between hubs and USB
devices. The entire tree can support up to 127 USB devices. The USB interface standard is intended
for keyboards, mice, modems, digitizer pads, and other low- to medium-speed peripherals.
Each USB interface is implemented as a two-wire differential pair for data, a power wire, a ground
wire, and a shield wire. The USB port signals appear on J24, the Utility2 connector, as shown in
Table 2– 18.
Table 2– 18. USB Port Pinout on Utility2 Connector
J24 Pin Signal Name Function
15 USBPWR1 USB1 +5 Volt Power
17 USBP-1 USB1 Data-
19 USBP+1 USB1 Data+
21 USBGND1 Ground
23 SHIELD1 Cable Shield for USB1
16 USBPWR2 USB2 +5 Volt Power
18 USBP-2 USB2 Data-
20 USBP+2 USB2 Data+
22 USBGND2 Ground
24 SHIELD2 Cable Shield for USB2
The bus can run at 12 Mbits/second or 1.5 Mbits/second, depending on a pull-up on the peripheral
device. A 1.5 KOhm pull-up on the +data line sets the speed to 12 Mbits/second. A 1.5 KOhm pull-
up on the -data line sets the speed to 1.5 Mbits/second.
The power to the peripheral device is current limited with a self-resetting fuse.