SAM7S256_14 Datasheet, PDF (517/775 Pages) ATMEL Corporation – ARM-based Flash MCU

Warning: Read, write operations to the UDP registers are allowed only if MCK is enabled for the UDP peripheral.
Switching off MCK for the UDP peripheral must be one of the last operations after writing to the and acknowledg-
ing the RXSUSP.
35.5.3.7 Receiving a Host Resume
In suspend mode, a resume event on the USB bus line is detected asynchronously, transceiver and clocks are dis-
abled (however the pullup shall not be removed).
Once the resume is detected on the bus, the WAKEUP signal in the UDP_ISR is set. It may generate an interrupt if
the corresponding bit in the UDP_IMR register is set. This interrupt may be used to wake up the core, enable PLL
and main oscillators and configure clocks.
Warning: Read, write operations to the UDP registers are allowed only if MCK is enabled for the UDP peripheral.
MCK for the UDP must be enabled before clearing the WAKEUP bit in the UDP_ICR register and clearing TXVDIS
in the UDP_TXVC register.
35.5.3.8 Sending a Device Remote Wakeup
In Suspend state it is possible to wake up the host sending an external resume.
• The device must wait at least 5 ms after being entered in suspend before sending an external resume.
• The device has 10 ms from the moment it starts to drain current and it forces a K state to resume the host.
• The device must force a K state from 1 to 15 ms to resume the host
To force a K state to the bus (DM at 3.3V and DP tied to GND), it is possible to use a transistor to connect a pullup
on DM. The K state is obtained by disabling the pullup on DP and enabling the pullup on DM. This should be under
the control of the application.
Figure 35-15. Board Schematic to Drive a K State
3V3
PIO
0: Force Wake UP (K State)
1: Normal Mode
1.5 K
DM
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
517