AT90USB646 datasheet(253/435 Pages) ATMEL

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7593D–AVR–07/06

AT90USB64/128

21.4

General Operating Modes

21.4.1

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 ID detection.

• If the ID pin is not connected to ground, the 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.

21.4.2

Power-on and reset

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

Figure 21-9. USB controller states after reset

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

• USBE is not set

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

• the macro is disabled,

• the pad is in the suspend mode,

• the Host and Device USB controllers internal states are reset.

• The DPACC bit and the DPADD10:0 field can be set by software. The DPRAM is not cleared.

• The SPDCONF bits can be set by software.

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

IP 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.

Dev ice

Reset

USBE=0

<anyother

state>

USBE=1

ID=1

Clockstopped

FRZCLK=1

Macrooff

USBE=0

Host

USBE=0

RESET

USBE=1

ID=0

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