AT43USB325 datasheet(92/109 Pages) ATMEL

92 / 109 page

3355C–USB–4/05

AT43USB325

8.5

Suspend and Resume

The AT43USB325 enters suspend only when requested by the USB host through bus inactivity

for at least 3 ms. The USB hardware would detect this request, sets the GLB_SUSP bit of

SPRSR, Suspend/Resume Register, and interrupts the microcontroller if the interrupt is enabled.

The microcontroller should shut down any peripheral activity and enter the Power Down mode

by setting the SE and SM bits of MCUCR and then executes the SLEEP instruction. The USB

hardware shuts off the oscillator and PLL.

8.5.1

Global Resume

Global resume is signaled by a J to K state change on Port0. The USB hardware enables the

oscillator/PLL, propagates the RESUME signaling, and sets the RSM bit of the SPRSR, which

generates an interrupt. The microcontroller starts executing where it left off and services the

interrupt. As part of the ISR, the firmware clears the GLB_SUSP bit.

8.5.2

Remote Wakeup

While the AT43USB325 is in global suspend, resume signaling is also possible through remote

wakeup if the remote wakeup feature is enabled. Remote wakeup is defined as a port connect,

port disconnect or resume signaling received at a downstream port or, in case of the embedded

function, through an external interrupt.

A remote wakeup initiated at a downstream port is similar in many respects to a global resume.

The USB hardware enables the oscillator/PLL, propagates the RESUME signaling, and sets the

RSM bit of the SPRSR which generates an interrupt. The microcontroller starts executing where

it left off and services the interrupt. As part of the ISR, the firmware clears the GLB_SUSP bit.

A remote wakeup from the embedded function is initiated through INT0 or the external interrupt,

INT1, which enables the oscillator/PLL and the USB hardware. The USB hardware drives

RESUME signaling and sets the FRMWUP and RSM bits of SPRSR which generates an inter-

rupt to the microcontroller. The microcontroller starts executing where it left off and services the

interrupt. As part of the ISR, the firmware clears the GLB SUSP bit.

At completion of RESUME signaling, the USB hardware sets the Port Suspend Status Change

bits of the Hub Port Status Change Registers.

8.5.3

Selective Suspend and Resume

See section on Hub Port Control Register, HPCON.

AT43USB325 Datasheet(PDF) 92 Page - ATMEL Corporation