Resume - NEC uPD98502 User Manual

The V 4120A is not permitted to write to other than USB Controller's USB General Mode Register and USB
R
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.
V 4120A
R
(6) R eceives U S B
interruption, reads
status register.
D etects transit to
R esum e state.
(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 V
"usbwakeup_p" signal instead of "URSM" bit.
(6) The V 4120A receives the interruption from USB Controller and, as a result, determines that the USB has
R
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.
CHAPTER 6 USB CONTROLLER
Figure 6-28. Resume Sequence
U S B
C ontroller
(4)
D etects R esum e
S ignaling, transits
to R esum e state.
(5)
S ets U R S M bit in
U S B G eneral
S tatus R egister 2
to a '1', and
issues the
interruption to
V 4120A .
R
µ
P D 98502
4120A. If clock supplement is stopped, V
R
Preliminary User's Manual S15543EJ1V0UM
H ost P C
(1) S tarts R esum e
S ignaling
20 m s
M ore than 20 m s
(2)
progress,stops
R esum e S ignaling
and executes
E O P S ignaling
for 2 bit-tim e
E nds of R esum e
(3)
processing
4120A has to check
R
365