Usb Operation (Suspend/Resume Function) - Renesas M16C Series User Manual

M30245 Group

2.8.4 USB Operation (Suspend/Resume Function)

The USB device has received the suspend signal from the host CPU following the power input state, and
then controls power supply and shifts the state into the suspend state.
And, by receiving the resume signal from the host CPU (or transmitting the resume signal to the host CPU
in the case of remote wakeup), it returns to the state before shifting into the suspend state and resumes
the USB communication.
This section explains how the M30245 group controls a shift into suspend state/recovery at the time of
resume in the state which the USB function control unit is enabled.
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(1) Related Registers
USB power management register
This register is used to control the suspend/resume by the USB function control unit.
• USB Suspend Status Flag
When the USB function control unit does not detected any bus activity on D+/D- line for at least 3ms,
the USB suspend status flag is set. Simultaneously, the USB suspend interrupt request occurs. This
flag is automatically cleared in the following cases:
- The active signal from the host CPU has been detected on the USB's D+/D- line. (When the
resume signal has been received and, simultaneously, the USB resume interrupt request has oc-
curred.)
- Transmission of the resume signal to the host CPU has been completed. (After USB remote
wakeup bit being set to "1", when clearing it to "0" to stop resume signal transmission.)
If the USB clock has been disabled during the suspend mode, this flag is not cleared until after the
USB clock is re-enabled.
• USB remote wakeup bit
When the USB suspend signal status flag is set to "1", the USB function control unit transmits the
resume signal to the host CPU while setting "1" to USB remote wakeup bit.
Set USB remote wakeup bit to "1" in order to transmit the resume signal to the host CPU and to return
to the previous state (remote wakeup) in the USB suspend state. Retain this bit at "1" for min. 1ms to
max. 15ms before completing the resume signal transmission by clearing to "0".
The configuration of USB power management register is shown in Figure 2.8.27.
Rev.2.00 Oct 16, 2006
REJ09B0340-0200
page 161 of 354
2. USB function