EZ-USB FX3 Technical Reference Manual, Document Number: 001-76074 Rev. *F 20
Introduction to EZ-USB FX3
(see Figure 1-1). The SuperSpeed bus employs a dual-simplex approach that allows simultaneous transmission and
reception of packets. In many cases, a SuperSpeed device may be both transmitting and receiving data at the same time. For
example, during burst transactions, a device may be receiving data from the host and returning acknowledgments associated
with the data it already received.
Figure 1-1. Cross-Section of a USB 3.0 Cable
Coming to the power distribution via the USB 3.0 host, 150 mA is considered as the unit load. USB 3.0 host supplies one unit
load of current for unconfigured devices and six unit loads of current for configured devices. The USB 3.0 host detects the
device connection based on the receiver end termination, and the transmitter is responsible for detecting the device
connection. USB 3.0 uses spread-spectrum clocking on its signaling. If spread-spectrum clocking is enabled, then the energy
of the signal is spread over a larger frequency band rather concentrated over a small frequency band at a high level, helping
to reduce the EMI emissions. The USB 3.0 physical layer supports low-frequency periodic signaling (LFPS), which is used to
manage signal initiation and low-power management on the bus on an idle link to consume less power. Ta b l e 1- 1 lists the
differences between the USB 3.0 and USB 2.0 physical layers.
Table 1-1. Differences Between Physical Layers of USB 3.0 and USB 2.0
1.1.2 Link Layer
The link layer is responsible for maintaining a reliable and robust communication channel between the host and the device.
The Link Training and Status State Machine (LTSSM) at the core of the USB 3.0 link layer establishes the link connectivity
Feature USB 3.0 USB 2.0
Signaling rate 5 Gbps 480 Mbps
Data transfers Dual simplex Half duplex
Number of pins in the USB cable
9 (VBUS, Ground, D+, D-, SSRX+, SSRX-, SSTX+, SSTX-,
Ground_Drain)
4 (VBUS, Ground, D+, D-)
Data lines in the cable Shielded differential pair (SDP, twisted, or twinax) Unshielded twisted pair (UTP)
Current supplied by the host
150 mA for unconfigured devices, 900 mA for configured
devices
100 mA for unconfigured devices, 500 mA for con-
figured devices
Device detection by the host Receiver end termination Pull-up resistor on D+ or D- lines
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