Specification
NET2272 USB Peripheral Controller
______________________________________________________________________________
NetChip Technology, Inc., 2003
Patent Pending
335 Pioneer Way, Mountain View, California 94041
TEL (650) 526-1490
FAX (650) 526-1494
http://www.netchip.com
Rev 1.2, October 15, 2003
51
7.1.2 Host-Initiated Wake-Up
The host may wake up the NET2272 by driving any non-idle state on the USB. The NET2272 will detect the host’s
wake-up request, and re-starts its internal oscillator. The host initiated wake-up is only recognized if the VBUS
input pin is high, and the USB Detect Enable and USB Root Port Wakeup Enable bits in the USBCTL0 register are
set.
7.1.3 Device-Remote Wake-Up
The device hardware signals a device remote wake-up by driving the CS# input pin low. If the I/O Wakeup Enable
bit in the USBCTL0 register is set, the NET2272 re-starts its local oscillator. Two milliseconds after the CS# pin is
asserted, the local CPU must write to the Generate Resume bit of the USBCTL1 register. This will cause a 10-ms
wake-up signal to be sent to the USB host.
7.1.4 Resume Interrupt
When the NET2272 begins either a Device-Remote Wake-Up or Host-Initiated Wake-Up, it may be programmed to
generate a resume interrupt. The Resume Interrupt bit of the IRQSTAT1 register is set when a resume is detected,
and can be enabled to generate an interrupt with the Resume Interrupt Enable bit.
7.2
NET2272 Power Configuration
The USB specification defines both bus-powered and self-powered devices. A bus-powered device is a peripheral
that derives all of its power from the upstream USB connector, while a self-powered device has an external power
supply.
The most significant consideration when deciding whether to build a bus-powered or a self-powered device is power
consumption. The USB specification dictates the following requirements for maximum current draw:
•
A device not configured by the host can draw only 100 mA from the USB power pins.
•
A device may not draw more than 500 mA from the USB connector’s power pins.
•
In suspend mode, the device may not draw more than 500
µA (or 2.5 mA for a high-power device)
from the USB connector’s power pins
If these power considerations can be met without the use of an external power supply, the device can be bus-
powered; otherwise a self-powered design should be implemented.
7.2.1 Self-Powered Device
Generally, a device with higher power requirements will be self-powered. In a self-powered device, the NET2272
VDD pins are powered by the local power supply. This allows the local bus to continue accessing the NET2272, even
when the device is not connected to the USB bus. The USB connector’s power pin is connected directly to the
NET2272 VBUS pin, and is only used to detect whether it is connected to a USB host.
While the device is connected to the USB, the NET2272 will automatically request suspend mode when appropriate.
The NET2272 should not be powered-down when its local bus is still connected to a powered-up device. There are
ESD protection circuits in the NET2272 that will short VDD pins to ground. If the VDD pins are not powered, they
will sink too much current from the board.
7.2.2 Low-Power Modes
7.2.2.1 USB Suspend (Unplugged from USB)
The NET2272 may draw a small amount of power when disconnected from the USB. Disconnecting from the USB
can be accomplished in two different ways:
•
Un-plug the USB cable.
•
Clear the USB Detect Enable bit in the USBCTL0 register.
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