Note
If your design does not use remote wakeup, tie the WAKEUP# pin high. Holding the
WAKEUP# pin low inhibits the EZ-USB chip from suspending.
When a USB device is suspended, the hub driver is tri-stated, and the bus pullup and pull-
down resistors cause the bus to assume the “J,” or idle state. A suspended device signals a
remote wakeup by asserting the “K” state for 10-15 ms. The 8051 controls this using the
SIGRSUME bit in the USBCS register.
If the 8051 finds WAKESRC=1 after exiting the idle mode, it drives the “K” state for 10-
15 ms to signal the USB remote wakeup. It does this by setting SIGRSUME=1, waiting
10-15 ms, and then setting SIGRSUME=0. When SIGRSUME=0, the EZ-USB bus buffer
reverts to normal operation. The resume routine should also write a “1” to the WAKESRC
bit to clear it.
J and K States
The USB Specification uses differential data signals D+ and D-. Instead of defining a
logical “1” and “0,” it defines the “J” and “K” states. For a high speed device, the “J”
state means (D+ > D-).
The USB Default device does not support remote wakeup. This fact is reported at enu-
meration time in byte 7 of the built-in Configuration Descriptor (Table 5-10).
Remote Wakeup: The Big Picture
Additional factors besides the EZ-USB suspend-resume mechanism described in this
section determine whether remote wakeup is possible. These are:
1. The device must report that it is capable of signaling a remote wakeup in the “bAt-
tributes” field of its Configuration Descriptor. See Table 5-10 for an example of this
descriptor.
2. The host must issue a “Set_Feature/Device” request with the feature selector field
set to 0x01 to enable remote wakeup. See Table 7-6 for the detailed request.
EZ-USB TRM v1.9
Chapter 11. EZ-USB Power Management
Page 11-5
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