466130 Datasheet, PDF (31/36 Pages) ATMEL Corporation – 8-bit Microcontroller with 64/128K Bytes of ISP Flash

ATmega32U6/AT90USB64/128
8.4 AT90USB1287/6 Third Release
• Incorrect CPU behavior for VBUSTI and IDTI interrupts routines
• 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. 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.
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. The internal USB engine remains in suspend mode but the USB differ-
ential receiver is still enabled and generates a typical 300µA extra-power consumption.
Detection of the suspend state after the transient perturbation should be performed by soft-
ware (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
100 ns negative spike occurs on SDA and SCL pins when TWI is enabled.
Problem Fix/workaround
No known workaround, enable ATmega32U6/AT90USB64/128 TWI first, before 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 sleep mode should be
disabled.
1. Asynchronous timer interrupt wake up from sleep generates multiple interrupts
If the CPU core is in sleep mode and wakes-up from an asynchronous timer interrupt and
then goes back into sleep mode, it may wake up multiple times.
Problem Fix/workaround
31
7593JS–AVR–03/09