466130 Datasheet, PDF (29/36 Pages) ATMEL Corporation – 8-bit Microcontroller with 64/128K Bytes of ISP Flash

ATmega32U6/AT90USB64/128
8.3 AT90USB1287/6 Second Release
• Incorrect CPU behavior for VBUSTI and IDTI interrupts routines
• USB Eye Diagram violation in low-speed mode
• Transient perturbation in USB suspend mode generates over consumption
• VBUS Session valid threshold voltage
• Spike on TWI pins when TWI is enabled
• High current consumption in sleep mode
• Async timer interrupt wake up from sleep generate multiple interrupts
7. Incorrect CPU behavior for VBUSTI and IDTI interrupts routines
The CPU core may incorrectly execute the interrupt vector related to the VBUSTI and IDTI
interrupt flags.
Problem fix/workaround
Do not enable these interrupts, firmware must process these USB events by polling VBUSTI
and IDTI flags.
6. 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.
5. 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.
4. VBUS Session valid threshold voltage
The VSession valid threshold voltage is internally connected to VBus_Valid (4.4V approx.).
That causes the device to attach to the bus only when Vbus is greater than VBusValid
instead of V_Session Valid. Thus if VBUS is lower than 4.4V, the device is detached.
Problem fix/workaround
According to the USB power drop budget, this may require connecting the device toa root
hub or a self-powered hub.
3. Spike on TWI pins when TWI is enabled
100 ns negative spike occurs on SDA and SCL pins when TWI is enabled.
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