AT90USB646 datasheet(246/456 Pages) ATMEL

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7593L–AVR–09/12

AT90USB64/128

22.4

General operating modes

22.4.1

Introduction

After a hardware reset, the USB controller is disabled. When enabled, the USB controller has to

run the Device Controller or the Host Controller. This is performed using the USB ID detection.

• If the ID pin is not connected to ground, the USB ID bit is set by hardware (internal pull up on

the UID pad) and the USB Device controller is selected

• The ID bit is cleared by hardware when a low level has been detected on the ID pin. The

Device controller is then disabled and the Host controller enabled

The software anyway has to select the mode (Host, Device) in order to access to the Device

controller registers or to the Host controller registers, which are multiplexed. For example, even

if the USB controller has detected a Device mode (pin ID high), the software shall select the

device mode (bit HOST cleared), otherwise it will access to the host registers. This is also true

for the Host mode.

Note:

For the Atmel AT90USB646/1286 products the Host mode is not included in the USB controller,

and the ID pin is not used and should be configured and used as a general I/O.

22.4.2

Power-on and reset

The next diagram explains the USB controller main states on power-on:

Figure 22-9. USB controller states after reset.

USB Controller state after an hardware reset is ‘Reset’. In this state:

• USBE is not set

• the USB controller clock is stopped in order to minimize the power consumption (FRZCLK=1)

• the USB controller is disabled

• the USB pad is in the suspend mode

• the Host and Device USB controllers internal states are reset

After setting USBE, the USB Controller enters in the Host or in the Device state (according to the

USB ID pin). The selected controller is ‘Idle’.

The USB Controller can at any time be ‘stopped’ by clearing USBE. In fact, clearing USBE acts

as an hardware reset.

Device

Reset

USBE=0

<any other

state>

USBE=1

ID=1

Clock stopped

FRZCLK=1

Macro off

USBE=0

Host

USBE=0

RESET

USBE=1

ID=0

AT90USB647/1287only

AT90USB646/1286forcedmode

AT90USB646 Datasheet(PDF) 246 Page - ATMEL Corporation

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