![](http://datasheet.mmic.net.cn/380000/-PD98501_datasheet_16745028/-PD98501_440.png)
CHAPTER 6 USB CONTROLLER
440
Preliminary User’s Manual S14767EJ1V0UM00
6.7 Power Management
USB Controller has a built in feature that allows it to use interrupts to inform the V
R
4120A RISC Processor of its
having received Suspend or Resume signaling from the Host PC. When the V
R
4120A Processor receives a Suspend
or Receive interrupt, it must perform the appropriate processing.
Also, for those instances when the port to which the
μ
PD98501 is connected is in the Suspend status (the
μ
PD98501 is in the Suspend status), USB Controller has a function for issuing Remote Wake Up signaling to switch
the Suspend status to Resume.
As a result, even if the
μ
PD98501 is in the Suspend status, data that arrives from the line (ADSL) is not discarded
but is instead can be passed to the Host PC.
The following sections explain each of the sequences.
6.7.1 Suspend
The Suspend sequence is as shown below.
Figure 6-26. Suspend Sequence
V
R
4120A
USB
Controller
Starts suspend.
Stops the
transaction on USB
3ms
If USB has no
activity for more
than 3ms, the
device connected
to USB transits in
Suspend state.
Sets USPD
bit(Bit16) in USB
General Status
Register 2 to
1 ,generates the
interruption to
V
R
4120A.
Receives USB
interruption,reads
status register.
Recognizes USB
became suspend
state
Host PC
(2)Transits in
suspend state,
because USB has
no activity for
more than 3ms.
(3)
(4)
(2)
(1)
μ
PD98501
(1) The host places the USB in the Suspend status. Traffic stops flowing through the USB.
(2) After 3 ms there is no traffic through the USB. Therefore, all of the devices connected to the USB shift to the
Suspend status. In the same way, USB Controller also enters the Suspend status. If DMA transfer is being
performed, however, USB Controller does not enter the Suspend status until after the completion of DMA
transfer.
(3) USB Controller makes the USPD bit (Bit16) of the USB General Status Register2 (Address: 18H) active, then
issues an interrupt to the V
R
4120A RISC Processor if interrupt is not masked.
(4) The V
R
4120A RISC Processor receives the interrupt from USB Controller, reads the USB General Status
Register2 and, as a result, determines that the USB is in the Suspend status.