HT45B0K Holtek Semiconductor, HT45B0K Datasheet - Page 18

• Manufacturer Part Number: HT45B0K
• Description: SPI to USB Bridge
• Manufacturer: Holtek Semiconductor

USB Module Suspend Mode and Wake-up
Rev 1.00
USB Suspend Mode
USB Host Wake-up
USB Remote Wake-up
If there is no signal on the USB bus for over 3ms, the devices will go into a suspend mode. The
Suspend indication bit SUSP, bit 0 of the USC register, will be set to 1 and a USB interrupt will
be generated to indicate that the device should jump to the suspend state to meet the 500μA USB
suspend current specification. In order to meet the 500μA suspend current, the firmware should
disable the USB clock by clearing the USB clock enable control bit USBCKEN in the UCC register
to 0. Also the USB PLL and PHY circuitry control bits known as PLL and SUSPC should be set to
1 to disable the USB PLL and PHY function. The suspend current is about 400μA.
When the resume signal is asserted by the USB host, the USB device will be woken up with a USB
interrupt generated on the INT line and the Resume indication bit RESUME in the USC register
will be set. In order to make the device function properly, the application program must set the
USBCKEN bit in the UCC register to 1 and clear the PLL and SUSPC bits in the USC register
and PIPE register respectively to 0. When the resume signal is de-asserted by the USB host, the
USB device actually leaves the suspend mode and the USB host will start to communicate with the
USB device. The SUSP bit will be cleared as well as the RESUME bit when the USB device really
leaves the suspend mode. So when the MCU is detecting the Suspend bit, the Resume bit should
be stored and taken into consideration. The following diagram shows the relationship between the
SUSP and RESUME bits and INT signal.
As the device has a remote wake-up function, it can wake up the USB Host by sending a wake-up
pulse by setting the RMWK bit in the USC register to 1 for 2μs and then setting the RMWK bit to 0.
Once the USB Host receives a wake-up signal from the device, it will send a Resume signal to the
device. The timing is as follows:
Suspend and Remote Wake-up
Suspend and Host Wake-up
18
2μs (Min.)
SPI to USB Bridge
HT45B0K
March 22, 2010
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