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29.4.4
Wake-up Function
To change a USB device from SUSPEND mode to WAKE UP mode, the USB protocol
provides 2 different options: Remote wake-up from device Wake-up from host PC and
Remote Wake-up
Host PC
Device
Device
Host PC
RESUM
STP
INT pin
A USB device must performed the following steps:
1. Exit the USB device from STOP mode through external interrupt.
2. Set UDCC:RESUM bit.
3. Clear UDCC:RESUM bit.
■ Wake-up from Host
Host PC
Device
WKUP
STP
For the devices, the following steps are required:
1. Oscillation stabilizing time setting must not exceed 10 ms.
2. WKUP interrupt triggers the entry into an interrupt routine that clears the WKUP flag of UDCS
(interrupt cause) and then returns to main program.
Figure 29.4-9 Remote Wake-up Operation
Suspend state
Oscillation
stabilization time
External interrupt
Figure 29.4-10 Wake-up Operation from Host
Suspend state
20ms
RESUME
RESUME
10ms
RESUM
Soft set, clear
not less than 20ms
RESUME
Oscillation
stabilization time
CHAPTER 29 USB FUNCTION
1ms
1ms
SOF
SOF
1ms
1ms
SOF
SOF
WKUP flag
Soft clear
761
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