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15.5.3
Suspend and Resume Operations
(1) Suspend Operation
If the USB bus enters the suspend state from a non-suspend state, perform the operation shown
in figure 15.8.
USB function
USB cable connected
A bus idle of 3 ms or
more occurs
A suspend/resume
interrupt occurs
Stop SOF marker function
Notes:
*1
The remote-wakeup function can be used only when it is enabled by the host. Accordingly, before using the remote-wakeup function,
check the RWUPs bit of the UDRR register. In an application that does not use the remote-wakeup function, the remote-function
enable need not be checked.
*2
Before entering the software standby state, USB module operation must be stopped by setting the MSTPB0 bit of MSTPCRB register
to 1.
Firmware
Clear SPRSi of UIFR3 to 0
Check if SPRSs of UIFR3
is set to 1
SOF marker
function enabled?
Yes
Stop SOF marker function
Clear SFME of UCTLR to 0
Remote wakeup
enabled
Is RWUPs of UDRR
set to 1?
Yes
Detect remote-wakeup
function enabled
Does system
enter power-down
mode?
Yes
Stop USB module
Set MSTPB0 of MSTPCRB to 1
Enter software standby
(only if necessary)
Wait for Suspend/resume /
interrupt
Figure 15.8 Suspend Operation
Check suspend state
No
*1
No
Detect remote-wakeup
function
No
*2
*2
Rev. 3.0, 10/02, page 489 of 686
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