© 2014 Exar Corporation
XR22801
9 / 40 exar.com/XR22801
Rev 1A
select their own product IDs. Additionally, upon request Exar will provide a selection of different product IDs for use with
Exar’s vendor ID for companies that do not wish to become members of USB.org, but wish to use their own product ID.
USB Suspend
All USB peripheral devices must support the USB suspend mode. Per USB standard, the XR22801 device will begin to
enter the suspend state if it does not detect any activity, (including Start of Frame or SOF packets) on its USB data lines for
3 ms. The peripheral device must then reduce power consumption from VBUS power within the next 7 ms to the allowed
limit of 2.5 mA per function for the suspended state. Because the XR22801 is a compound device with 5 functions, the sus-
pend state power limit is 12.5 mA for the device. Note that in this context, the "device" is all circuitry (including the XR22801)
that draws power from the host VBUS.
Remote Wakeup
When the XR22801 is suspended, the E0/RI#/RWK#/G0 pin may be used to request that the host exit the Suspend state if
it is configured as an input. A high to low transition on this pin will cause the device to signal a remote wakeup request to the
host via Exar’s custom driver. Note that the CDC-ACM driver does not support the remote wakeup feature. The E0/GPIO0/
RI#/RWK# pin may be used to signal remote wakeup by default. Additionally, the E6/RX/RWK# pin, if configured as an
input, may also be used for remote wakeup if enabled using the REMOTE_WAKEUP register. The Ethernet function in the
XR22801 can also be used for remote wakeup under certain conditions. Refer to Ethernet Remote Wakeup on page 10.
USB Strings
USB specifies three character string descriptors that are provided to the USB host during enumeration in string descriptors:
the manufacturer, product and serial strings. In a compound device such as the XR22801, each function provides these
strings to the USB host. The default manufacturer string for the XR22801 device is "Exar Corp.". The default product strings
for the hub, Ethernet function, UART function, I
2
C function and EDGE function are shown in Table 2. The serial number
string is a unique alpha-numeric ASCII string programmed into the device at the factory.
The OTP may be used to override these strings. However, to ensure unique serial numbers for each device, it is recom-
mended that the factory pre-programmed serial number string be used and not be overwritten via OTP.
Table 1: Default XR22801 Product IDs
XR22801 Function Default Product ID
Hub 0x0801
Ethernet 10/100 0x1300
UART 0x1400
I
2
C
0x1100
EDGE 0x1200
Table 2: Default XR22801 Product Strings
XR22801 Function Default Product String
Hub Exar’s XR22801 Hub
Ethernet 10/100 Exar USB Ethernet
UART Exar USB UART
I
2
CExar USB I
2
C
EDGE Exar USB EDGE
