Datasheet

7593LS–AVR–09/12

AT90USB64/128

9.2.3 Atmel AT90USB646/7 Second Release.

• USB Eye Diagram violation in low-speed mode

• Transient perturbation in USB suspend mode generates over consumption

• Spike on TWI pins when TWI is enabled

• High current consumption in sleep mode

• Async timer interrupt wake up from sleep generate multiple interrupts

5. USB Eye Diagram violation in low-speed mode

The low to high transition of D- violates the USB eye diagram specification when transmitting

with low-speed signaling.

Problem fix/workaround

None.

4. Transient perturbation in USB suspend mode generates overconsumption

In device mode and when the USB is suspended, transient perturbation received on the

USB lines generates a wake up state. However the idle state following the perturbation does

not set the SUSPI bit anymore. The internal USB engine remains in suspend mode but the

USB differential receiver is still enabled and generates a typical 300µA extra-power con-

sumption. Detection of the suspend state after the transient perturbation should be

performed by software (instead of reading the SUSPI bit).

Problem fix/workaround

USB waiver allows bus powered devices to consume up to 2.5mA in suspend state.

3. Spike on TWI pins when TWI is enabled

100ns negative spike occurs on SDA and SCL pins when TWI is enabled.

Problem fix/workaround

No known workaround, enable Atmel AT90USB64/128 TWI first versus the others nodes of

the TWI network.

2. High current consumption in sleep mode

If a pending interrupt cannot wake the part up from the selected mode, the current consump-

tion will increase during sleep when executing the SLEEP instruction directly after a SEI

instruction.

Problem fix/workaround

Before entering sleep, interrupts not used to wake up the part from the sleep mode should

be disabled.

1. Asynchronous timer interrupt wake up from sleep generates multiple interrupts

If the CPU core is in sleep and wakes-up from an asynchronous timer interrupt and then go

back in sleep mode again it may wake up several times.

Problem fix/workaround

A softw are w orkaround is to w ait w ith performing the sleep instruction until

TCNT2>OCR2+1.