ATXMEGA256A3_1012 Datasheet, PDF (122/134 Pages) ATMEL Corporation – 8/16-bit XMEGA A3 Microcontroller

8068T–AVR–12/10
XMEGA A3
Problem fix/Workaround
Wait at least one prescaled RTC clock cycle before reading the RTC CNT value.
22. Pending asynchronous RTC-interrupts will not wake up device
Asynchronous Interrupts from the Real-Time-Counter that is pending when the sleep
instruction is executed, will be ignored until the device is woken from another source or the
source triggers again.
Problem fix/Workaround
None.
23. TWI Transmit collision flag not cleared on repeated start
The TWI transmit collision flag should be automatically cleared on start and repeated start,
but is only cleared on start.
Problem fix/Workaround
Clear the flag in software after address interrupt.
24. Clearing TWI Stop Interrupt Flag may lock the bus
If software clears the STOP Interrupt Flag (APIF) on the same Peripheral Clock cycle as the
hardware sets this flag due to a new address received, CLKHOLD is not cleared and the
SCL line is not released. This will lock the bus.
Problem fix/Workaround
Check if the bus state is IDLE. If this is the case, it is safe to clear APIF. If the bus state is
not IDLE, wait for the SCL pin to be low before clearing APIF.
Code:
/* Only clear the interrupt flag if within a "safe zone". */
while ( /* Bus not IDLE: */
((COMMS_TWI.MASTER.STATUS & TWI_MASTER_BUSSTATE_gm) !=
TWI_MASTER_BUSSTATE_IDLE_gc)) &&
/* SCL not held by slave: */
!(COMMS_TWI.SLAVE.STATUS & TWI_SLAVE_CLKHOLD_bm)
)
{
/* Ensure that the SCL line is low */
if ( !(COMMS_PORT.IN & PIN1_bm) )
if ( !(COMMS_PORT.IN & PIN1_bm) )
break;
}
/* Check for an pending address match interrupt */
if ( !(COMMS_TWI.SLAVE.STATUS & TWI_SLAVE_CLKHOLD_bm) )
{
/* Safely clear interrupt flag */
COMMS_TWI.SLAVE.STATUS |= (uint8_t)TWI_SLAVE_APIF_bm;
}
25. TWI START condition at bus timeout will cause transaction to be dropped
If Bus Timeout is enabled and a timeout occurs on the same Peripheral Clock cycle as a
START is detected, the transaction will be dropped.
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