EZ-USB FX3 Technical Reference Manual, Document Number: 001-76074 Rev. *F 91
Universal Serial Bus (USB)
packet is received correctly, and their corresponding interrupts are generated if not masked. Upon receipt of a SetAddress
command from the host, the DEV_CS register field DEVICEADDR is updated with the new device address.
6.7.10 IN Packet
IN packets are received by the SIE and reported to the TP, which generates the appropriate responses to the SIE and
updates the corresponding DEV_EPO_CS register for the endpoint to which the packet was sent.
6.7.11 OUT Packet
OUT packets are received by the SIE and reported to the TP, which generates the appropriate responses to the SIE and
updates the corresponding DEV_EPO_CS register for the endpoint to which the packet was sent.
6.8 USB 3.0 and USB 2.0 Function Coordination
When the FX3 is functioning as a USB device, the USB 3.0 PHY or the USB 2.0 PHY needs to be turned on based on the
capabilities of the USB host to which FX3 is connected. The USB 3.0 specification requires that only one of the PHY layers be
operational at most times during the USB device operation. The exception to this rule is a small time window in which the
device is attempting to move from USB 2.0 mode to USB 3.0 mode. The firmware application on FX3 is responsible for
identifying the host capabilities and setting the USB connection accordingly. The following procedure should be used by the
FX3 firmware for USB connection negotiation:
1. Wait for a valid VBus voltage (GCTL_IOPWR interrupt).
2. Turn on the USB 3.0 PHY to start 3.0 receiver detection.
a. If receiver detection succeeds, the LNK_LTSSM_CONNECT interrupt will be received. If this interrupt is received, the
device will proceed with enumeration in USB 3.0 mode.
3. If receiver detection fails, the LNK_LTSSM_DISCONNECT interrupt will be received. If this interrupt is received:
a. Turn off USB 3.0 PHY and turn on USB 2.0 PHY.
b. A USB 2.0 bus reset will be received as part of USB 2.0 connection startup.
c. The 3.0 PHY should be re-enabled on receiving the URESET interrupt that is triggered on a 2.0 bus reset. Both the 2.0
and 3.0 PHYs will be active at this time.
d. If the 3.0 receiver detection succeeds (LNK_LTSSM_CONNECT):
i.Turn off the USB 2.0 PHY.
ii.Proceed with enumeration as a USB 3.0 device.
e. If the 3.0 receiver detection fails (LNK_LTSSM_DISCONNECT):
i.Turn off the USB 3.0 PHY.
ii.Check number of times that 3.0 receiver detection has failed. If this count is greater than 3:
4. Proceed with enumeration as a USB 2.0 device.
5. There is no need to attempt 3.0 enumeration on any further bus resets.
Any PHYs that are enabled need to be disabled when the VBus voltage is removed. The entire previous procedure needs to
be repeated when valid VBus is detected again.
Note that USB 3.0 PHY on the FX3 needs to be turned off when VBus is removed or a host disconnect is discovered by other
means. If the 3.0 PHY is left turned on, the 3.0 link startup is liable to fail when connected again to the host.
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