SAM7X128_14 Datasheet, PDF (617/662 Pages) ATMEL Corporation – ARM-based Flash MCU

41.3.9.5 TWI: Software Reset
when a software reset is performed during a frame and when TWCK is low, it is impossible to initiate a new transfer in
READ or WRITE mode.
Problem Fix/Workaround
None.
41.3.10 Universal Synchronous Asynchronous Receiver Transmitter (USART)
41.3.10.1 USART: CTS in Hardware Handshaking
When Hardware Handshaking is used and if CTS goes low near the end of the start bit, a character can be lost.
CTS must not go high during a time slot occurring between 2 Master Clock periods before and 16 Master Clock periods
after the rising edge of the start bit.
Problem Fix/Workaround
None.
41.3.10.2 USART: Hardware Handshaking – Two Characters Sent
If CTS switches from 0 to 1 during the TX of a character and if the holding register (US_THR) is not empty, the content of
US_THR will also be transmitted.
Problem Fix/Workaround
Don't use the PDC in transmit mode and do not fill US_THR before TXEMPTY is set at 1.
41.3.10.3 USART: RXBRK Flag Error in Asynchronous Mode
In receiver mode, when there are two consecutive characters (without time guard in between), RXBRK is not taken into
account. As a result, the RXBRK flag is not enabled correctly and the frame error flag is set
Problem Fix/Workaround
Constraints on the transmitter device connected to the SAM7X USART receiver side:
The transmitter may use the timeguard feature or send two STOP conditions. Only one STOP condition is taken into
account by the receiver state machine. After this STOP condition, as there is no valid data, the receiver state machine
will go in idle mode and enable the RXBRK flag.
41.3.10.4 USART: DCD is Active High instead of Low.
The DCD signal is active at High level in the USART Modem Mode .
DCD should be active at Low level.
Problem Fix/Workaround
Add an inverter.
SAM7X Series [DATASHEET]
6120K–ATARM–11-Feb-14
617