SIGRWU
Meaning:
Signal Remote Wakeup.
Location:
USBCTL.2
Set:
The CPU sets this bit to signal remote wakeup to the USB host.
Clear:
The CPU clears this bit to terminate remote wakeup signaling.
POR:
SIGRWU=0
Chip Reset:
No change
Bus Reset:
No change
Pwr Down:
Read-write
Programming Notes:
The SPI master sets this bit to initiate USB Remote Wakeup signaling on the bus. When the SPI
master sets SIGRWU=1 the MAX3420E waits for 5 milliseconds of a J-state, and then drives the
bus with the K-state (D+ low, D- high) for 10 milliseconds. After the 10 millisecond interval, the
MAX3420E stops driving the bus and asserts the RWUDNIRQ (page 57) interrupt bit. The SPI
master should set SIGRWU=1 only when the bus is in the suspended state.
If the SPI master writes the USBCTL register with SIGRWU=1 while the MAX3420E is in its
power-down state (PWRDOWN=1, page 55) the write to the USBCTL register should also have
the PWRDOWN bit cleared to restart the internal oscillator. In this case SIE restarts its oscillator
and waits for it to stabilize before initiating the RWU signaling.
The SPI master sets SIGRWU=1 and waits for the SIE to assert the RWUDNIRQ (page 57) to
indicate that the signaling interval is over. When RWUDNIRQ asserts, the SPI master should set
SIGRWU=0 to turn off the signaling. If the SPI master sets SIGRWU=0 during the 10 msec
signaling interval, the RWU signal still terminates after the full 10 msec. If the SPI master does
not clear the SIGRWU bit when the RWUDNIRQ interrupt asserts, the SIE continuously drives
the bus with 5 msec float (J), 10 msec K.
FYI:
A USB peripheral should signal remote wakeup only if two pre-conditions are met:
1. During enumeration the device firmware informs the host that the device is capable of
signaling remote wakeup. Specifically, the bmAttributes field of the Configuration
Descriptor uses bit 5 to indicate if a configuration supports remote wakeup: 1=yes, 0=no.
2. The host issues a Set_Feature request with the feature selector field set to
“Device_Remote_Wakeup”. The host would never issue this request if it found the first
condition, remote-wakeup-capable, to be false.
The host can later inhibit remote wakeup signaling by issuing a Clear_Feature request with the
selector field set to “Device_Remote_Wakeup”.
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