net2890 ETC-unknow, net2890 Datasheet - Page 34

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

Specification
4.10 Root Port Reset
If the SIE in the NET2890 detects a single-ended zero on the root port for greater than 2.5 microseconds, it
is interpreted as a root port reset. The LRESET# output pin is asserted, and the following resources are
reset:
The remainder of the configuration registers are not affected by the root port reset.The Root Port Reset
Interrupt Status bit is set when a root port reset has been detected, and if enabled, a local interrupt is
generated. The local CPU should take appropriate action when this interrupt occurs.
According the the USB Specification, the width of the USB reset is minimally 10ms and may be longer
depending on the upstream host or hub. There is no specified maximum width for the USB reset. The
LRESET# pin is asserted while the USB reset is active, and is negated a few 48 MHz clocks after the USB
reset condition is removed by the host.
4.11 NET2890 Power Configuration
The USB specification defines both bus-powered and self-powered devices. A bus-powered device is a
peripheral which derives all of its power from the upstream USB connector, while a self-powered device
has an external power supply. The NET2890 is well-suited for both types of applications.
The most significant consideration when deciding whether to build a bus-powered or a self-powered device
is power consumption. The USB specification lays out the following requirements for maximum current
draw:
If these power considerations can be met without the use of an external power supply, the peripheral can be
bus-powered; otherwise a self-powered design should be implemented.
4.11.1 Bus-Powered Device
If the local bus is powered at 3.3 Volts, the V
regulated source derived from the USB 5.0 volt power pin. For a 5.0 volt local bus, the V
connected directly to the USB 5.0 Volt power pin, while the V
through a regulator. The rest of the local-side circuitry is also connected to the USB power pin, either
through a regulator or directly. Therefore, the peripheral’s local circuitry and the NET2890 will all power
up simultaneously, and initialization can occur normally with a power-on reset.
4.11.2 Self-Powered Device
Generally, a peripheral with higher power requirements will be self-powered. In a self-powered device, the
NET2890 V
bus to continue accessing the NET2890, even when the device is not connected to the USB bus. The USB
connector’s power pin is left unconnected.
____________________________________________________________________________________
DD
SIE
USB state machines
Local state machines
Our Address Register
Device Configured bit of Main Control Register.
FIFOs and FIFO Valid bits
A peripheral 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 peripheral may not draw more than 500 A from the USB connector’s
power pins
and V
DDL
pins of the NET2890 are powered by the local power supply. This allows the local
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DD
and V
DDL
pins of the device are connected to a 3.3 Volt
DD
pins must still be connected to 3.3 Volts
NET2890 USB Interface Controller
DDL
pin may be
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