AT43USB325E-AC datasheet(85/109 Pages) ATMEL

85 / 109 page

3355C–USB–4/05

AT43USB325

These bits define which port is being addressed for the command defined by bits [2:0].

8.4.3

Selective Suspend and Resume

The host can selectively suspend and resume a port through the Set Port Feature

(PORT_SUSPEND) and Clear Port Feature (PORT_SUSPEND).

A port enters the suspend state after the microcontroller interprets the suspend request and sets

the appropriate bits of the Hub Port Control Register, HPCON. From this point on he hub

repeater hardware is responsible for proper actions in placing Ports 2:5 in the suspend mode.

For Port 1, the embedded function port, the hardware will stop responding to any normal bus

traffic, but the microcontroller firmware must place all external circuitry associated with the func-

tion in the low-power state.

A po rt ex its f rom the susp en d sta te wh en t he h ub rece ives a C le ar Po rt F ea tur e

(PORT_SUSPEND) or Set Port Feature (PORT_RESET). If the Clear Port Feature

(PORT_SUSPEND) is directed towards Ports 2:5, the USB hardware drives a “K” downstream

for at least 20 ms followed by a low speed EOP. It then places the port in the enabled state. A

Clear Port Feature (PORT_SUSPEND) to Port 1 (the embedded function) causes the firmware

to wait 20 ms, take the embedded function out of the suspended state and then enable the port.

The ports can also exit from the suspended state through a remote wakeup if this feature is

enabled. For Ports 2:5, this means detection of a connect/disconnect or an upstream directed J

to K signaling. Remote wakeup for the embedded function is initiated through a key depression

which triggers a KB INT.

Bit2

Bit1

Bit0

Port addresses

101

Port5

100

Port4

011

Port3

010

Port2

AT43USB325E-AC Datasheet(PDF) 85 Page - ATMEL Corporation