Suspend Function - Fujitsu F2MC-16LX Hardware Manual

CHAPTER 13 USB FUNCTION
13.4.2

Suspend Function

A USB device must have a configuration of bus power supply where power
consumption is 500µA or less in suspend status. The section covers a USB device from
its transmitting to suspend status to its entering STOP mode.
Suspend Processing
When the USB device core detects suspend status, SUSP of the UDCS register is set to be enabled.
The following shows an example of the suspend processing:
Host PC
Device
SUSP
STP
Suspend processing
The USB Function determines that it detects suspend status when there is no operation for not less than
3 ms on the USB bus, and the SUSP interrupt cause in the UDCS register is set. If a USB device supports
remote wake-up, the USB Function waits another 2 ms (which blocks remote wake-up during this time
period), and set the device to stop mode.
302
Figure 13.4-6 Suspend Operation
1ms 1ms 3ms
SOF SOF SOF
Suspend state
Remote wake-up support
2ms
SUSP flag
Soft clear