SAM7S256_14 Datasheet, PDF (640/775 Pages) ATMEL Corporation – ARM-based Flash MCU

40.8.8.2 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.
40.8.8.3 TWI: Disabling Does not Operate Correctly
Any transfer in progress is immediately frozen if the Control Register (TWI_CR) is written with the bit MSDIS at 1.
Furthermore, the status bits TXCOMP and TXRDY in the Status Register (TWI_SR) are not reset.
Problem Fix/Workaround
The user must wait for the end of transfer before disabling the TWI. In addition, the interrupts must be disabled
before disabling the TWI.
40.8.8.4 TWI: NACK Status Bit Lost
During a master frame, if TWI_SR is read between the Non Acknowledge condition detection and the TXCOMP bit
rising in the TWI_SR, the NACK bit is not set.
Problem Fix/Workaround
The user must wait for the TXCOMP status bit by interrupt and must not read the TWI_SR as long as transmission
is not completed.
TXCOMP and NACK fields are set simultaneously and the NACK field is reset after the read of the TWI_SR.
40.8.8.5 TWI: Possible Receive Holding Register Corruption
When loading the TWI_RHR, the transfer direction is ignored. The last data byte received in the TWI_RHR is cor-
rupted at the end of the first subsequent transmit data byte. Neither RXRDY nor OVERRUN status bits are set if
this occurs.
Problem Fix/Workaround
The user must be sure that received data is read before transmitting any new data.
40.8.9 Universal Synchronous Asynchronous Receiver Transmitter (USART)
40.8.9.1 USART: CTS in Hardware Handshaking
When Hardware Handshaking is used and if CTS goes low near the end of the starting bit, a character can be lost.
Problem Fix/Workaround
CTS must not go low during a time slot occurring between 2 Master Clock periods before the starting bit and 16
Master Clock periods after the rising edge of the starting bit.
40.8.9.2 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 con-
tent 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.
40.8.9.3 USART: XOFF Character Bad Behavior
The XOFF character is sent only when the receive buffer is detected full. While the XOFF is being sent, the remote
transmitter is still transmitting. As only one Holding register is available in the receiver, characters will be lost in
reception. This makes the software handshaking functionality ineffective.
Problem Fix/Workaround
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
640