NET2890 datasheet(35/73 Pages) ETC

35 / 73 page

Specification

NET2890 USB Interface Controller

____________________________________________________________________________________

NetChip Technology, Inc., 1999

335 Pioneer Way, Mountain View, California 94041

TEL (650) 526-1490

FAX (650) 526-1494

http://www.netchip.com

Rev 2.0, Draft 9, July 16, 1999

While the peripheral is connected to the USB, the NET2890 will automatically request suspend mode when

appropriate, as described in section 4.9.

The NET2890 should not be powered-down when its local bus is still connected to a powered-up device.

There are ESD protection circuits in the NET2890 which will short Vcc pins to ground. If the Vcc pins are

not powered, they will sink too much current from the board.

4.11.3 Low-Power Modes

4.11.3.1 USB Suspend (Unplugged from USB)

The NET2890 may draw a small amount of power when un-plugged from the USB. In power-sensitive

applications, the local CPU can force the NET2890 to enter low-power suspend mode when unplugged

from the USB by setting the Suspend Control Bit. The NET2890 will automatically wake-up when the

peripheral is re-connected to the USB. Do not force suspend mode unless the peripheral is unplugged from

the USB. When the NET2890 is connected to the USB, it is a violation of the USB specification to enter the

suspend state unless the upstream port has been idle for at least 3 milliseconds.

This is the preferred method of suspending the NET2890, since a USB plug-in will automatically cause the

NET2890 to wake-up and set the Resume Interrupt Status bit.

4.11.3.2 Power-On Standby

The peripheral can prevent the NET2890 from starting its oscillator on power-up by driving a LOW into the

USBOE# pin from an external open-drain source while RESET# is asserted (LOW). In this state the

NET2890 requires only a small quiescent standby current.

When the peripheral wishes to start the oscillator, it releases the USBOE# line and continues to assert

RESET# for a minimum of 2 milliseconds. Note that while the oscillator is stopped, the NET2890 cannot

respond to USB requests, so the oscillator must be allowed to start when the peripheral detects a USB plug-

in event. Note also that USBOE# should only be driven from an external source while RESET# is asserted.

The NET2890 will not detect a USB plug-in event while in this standby state. The device is responsible for

detecting the plug-in, and ending the standby condition. This standby technique is appropriate when the

device’s power budget does not allow the NET2890 to be active long enough to shut it down by setting the

Suspend Control Bit.

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