net2890 ETC-unknow, net2890 Datasheet - Page 33

• Manufacturer Part Number: net2890
• Description: Interface Controller
• Manufacturer: ETC-unknow

Specification
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 A 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:
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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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 A of current is drawn from the USB
power bus.
The local CPU writes a 1 to the Suspend Control Bit to initiate the suspend.
335 Pioneer Way, Mountain View, California 94041
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NetChip Technology, Inc., 1999
Rev 2.0, Draft 9, July 16, 1999
http://www.netchip.com
NET2890 USB Interface Controller
33