NET2890 datasheet(33/73 Pages) ETC

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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

4.9 Suspend Mode

When there is a three millisecond period of inactivity on the USB, the USB specification requires a device

to enter into a low-power suspended state. The device may not draw more than 500

µA of current while in

this state. To facilitate this, the NET2890 provides a Suspend Request Interrupt Status bit and a

Suspend Control bit. Additionally, the NET2890 allows local bus hardware to initiate a “device remote

wake-up” to the USB.

4.9.1 The Suspend Sequence

The typical sequence of a suspend operation is as follows:

•

During device configuration, the local CPU enables the Suspend Request Interrupt Status bit to

generate a local interrupt.

•

When the USB is idle for three milliseconds, the NET2890 sets the Suspend Request Interrupt

Status bit, generating an interrupt to the local CPU. This interrupt can also occur if the NET2890 is

not connected to a host, and the USB data lines are pulled to the idle state (DP high, DM low).

•

The local CPU accepts this interrupt by clearing the Suspend Request Interrupt Status bit, and

performs the tasks required to ensure that not more than 500

µA of current is drawn from the USB

power bus.

•

The local CPU writes a 1 to the Suspend Control Bit to initiate the suspend.

In suspend mode, the NET2890’s oscillator shuts down, and most output pins are tri-stated to conserve

power (see section 3, Pin Description). As the NET2890 enters the suspend state, the SUSP# output pin

will be driven low for 20 nsec and then floated. It has an internal pull-down resistor to keep it low during

suspend. Note that input pins on the NET2890 which do not have an internal pull-up or pull-down resistors

should not be allowed to float during suspend mode. The NET2890 will leave suspend mode by detecting a

host initiated wake-up or by a device remote wake-up.

If a device is self-powered, it may ignore the USB suspend request and never set the Suspend Control

(IRQSTAT2[4]) bit.

4.9.2 Host-Initiated Wake-Up

The host may wake up the NET2890 by driving any non-idle state on the USB. The NET2890 will detect

the host’s wake-up request, and re-starts its internal oscillator. Two milliseconds later, the SUSP# output

signal is driven high to indicate that the NET2890 has completed its wake-up.

4.9.3 Device-Remote Wake-Up

The device hardware signals a device remote wake-up by driving the WAKEUP# input pin low. If the

Device Remote Wake-up Enable bit is set, the NET2890 will send a 10-ms wake-up signal to the USB

host, and concurrently re-start its local oscillator. Two milliseconds after the WAKEUP# pin is asserted,

the SUSP# line is driven high to indicate that the NET2890 has completed its wake-up.

4.9.4 Resume Interrupt

When the NET2890 begins either a Device-Remote Wake-Up or Host-Initiated Wake-Up, it may be

programmed to generate a resume interrupt. The Resume Interrupt Status bit is set when a resume is

detected, and can be enabled to generate an interrupt with the Resume Interrupt Enable bit.

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