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
52
In power-sensitive applications, the local CPU can force the NET2272 to enter low-power suspend mode when
disconnected from the USB by writing a 1 to the Suspend Request Interrupt bit. The NET2272 will automatically
wake-up when the peripheral is re-connected (cable plugged in and USB Detect Enable bit set) to the USB. Do not
force suspend mode unless the peripheral is disconnected from the USB. When the NET2272 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 NET2272, since a USB re-connection will automatically cause the
NET2272 to wake-up and set the Resume Interrupt bit.
7.2.2.2 Power-On Standby
The local CPU can prevent the NET2272 from starting its oscillator on power-up by driving a LOW into the CS#
pin while RESET# is asserted (LOW). In this state the NET2272 requires only a small quiescent standby current.
When the peripheral wishes to start the oscillator, it releases the CS# pin and continues to assert RESET# for a
minimum of 2 milliseconds. Note that while the oscillator is stopped, the NET2272 cannot respond to USB
requests, so the oscillator must be allowed to start when the peripheral detects a USB connection event. The local
CPU is responsible for detecting the connection, and ending the standby condition.
This standby technique is appropriate when the device’s power budget does not allow the NET2272 to be active
long enough to shut it down by setting the Suspend Request Interrupt bit.
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