CHAPTER 6 USB CONTROLLER
Preliminary User’s Manual S15543EJ1V0UM 365
The VR4120A is not permitted to write to other than USB Controller's USB General Mode Register and USB
Interrupt Mask Register 2 while USB Controller is in the Suspend status. Otherwise, after USB Controller enters the
Resume status, its operation will be unpredictable.
6.7.2 Resume
The Resume sequence is shown below.
Figure 6-28. Resume Sequence
VR4120A USB
Controller
Starts Resum e
Signaling
(1)
20 ms
More than 20 ms
progress,stops
Resume Signaling
and executes
EOP Signaling
for 2 bit-time
Sets URSM bit in
USB General
Status Register 2
to a '1', and
issues the
interruption to
VR4120A.
Receives USB
interruption, reads
status register.
Detects trans it to
Resume state.
Host PC
Detects Resume
Signaling, transits
to Resume state.
Ends of Resume
processing
(2)
(3)
(4)
(5)
(6)
µ
PD98502
(1) The Host PC starts Resume Signaling. The Resume Signaling is passed to every device connected to the
USB.
(2) After at least 20 ms have elapsed, the Host PC stops the Resume Signaling then performs EOP Signaling for a
2bit-time duration.
(3) This causes the Host PC to terminate its Resume processing.
(4) USB Controller receives the Resume Signaling.
(5) USB Controller sets the URSM bit (Bit 18) of the USB General Status Register 2 (Address: 1000_1018H) to a
‘1’, then issues an interruption to the VR4120A. If clock supplement is stopped, VR4120A has to check
“usbwakeup_p” signal instead of “URSM” bit.
(6) The VR4120A receives the interruption from USB Controller and, as a result, determines that the USB has
entered the Resume status.
After USB Controller enters the Resume status, it continues with the transmit/receive processing it was performing
immediately before it entered the Suspend status.