NEC Network Controller uPD98502 - Manual (Page 365)

CHAPTER 6 USB CONTROLLER
Preliminary User’s Manual S15543EJ1V0UM 365
The V R 4120A 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
V R 4120A U S B
C ontroller
S tarts R esum e
S ignaling
(1)
20 m s
M ore than 20 m s
progress,stops
R esum e S ignaling
and executes
E O P S ignaling
for 2 bit-tim e
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 R 4120A .
R eceives U S B
interruption, reads
status register.
D etects transit to
R esum e state.
H ost P C
D etects R esum e
S ignaling, transits
to R esum e state.
E nds of R esum e
processing
(2)
(3)
(4)
(5)
(6)
µ P D 98502
(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
R
4120A. If clock supplement is stopped, V
R
4120A has to check
“usbwakeup_p” signal instead of “URSM” bit.
(6) The V
R
4120A 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.