Atmel ARM-Based Evaluation Kit AT91SAM9N12-EK AT91SAM9N12-EK Data Sheet
Product codes
AT91SAM9N12-EK
777
SAM9N12/SAM9CN11/SAM9CN12 [DATASHEET]
11063K–ATARM–05-Nov-13
When the USART is the receiver and it detects an error, it does not load the erroneous character in the Receive Holding
Register (US_RHR). It appropriately sets the PARE bit in the Status Register (US_SR) so that the software can handle
the error.
Register (US_RHR). It appropriately sets the PARE bit in the Status Register (US_SR) so that the software can handle
the error.
Figure 40-30. T = 0 Protocol without Parity Error
Figure 40-31. T = 0 Protocol with Parity Error
Receive Error Counter
The USART receiver also records the total number of errors. This can be read in the Number of Error (US_NER) register.
The NB_ERRORS field can record up to 255 errors. Reading US_NER automatically clears the NB_ERRORS field.
The NB_ERRORS field can record up to 255 errors. Reading US_NER automatically clears the NB_ERRORS field.
Receive NACK Inhibit
The USART can also be configured to inhibit an error. This can be achieved by setting the INACK bit in the Mode
Register (US_MR). If INACK is to 1, no error signal is driven on the I/O line even if a parity bit is detected.
Register (US_MR). If INACK is to 1, no error signal is driven on the I/O line even if a parity bit is detected.
Moreover, if INACK is set, the erroneous received character is stored in the Receive Holding Register, as if no error
occurred and the RXRDY bit does rise.
occurred and the RXRDY bit does rise.
Transmit Character Repetition
When the USART is transmitting a character and gets a NACK, it can automatically repeat the character before moving
on to the next one. Repetition is enabled by writing the MAX_ITERATION field in the US_MR at a value higher than 0.
Each character can be transmitted up to eight times; the first transmission plus seven repetitions.
on to the next one. Repetition is enabled by writing the MAX_ITERATION field in the US_MR at a value higher than 0.
Each character can be transmitted up to eight times; the first transmission plus seven repetitions.
If MAX_ITERATION does not equal zero, the USART repeats the character as many times as the value loaded in
MAX_ITERATION.
MAX_ITERATION.
When the USART repetition number reaches MAX_ITERATION, the ITERATION bit is set in the Channel Status Register
(US_CSR). If the repetition of the character is acknowledged by the receiver, the repetitions are stopped and the iteration
counter is cleared.
(US_CSR). If the repetition of the character is acknowledged by the receiver, the repetitions are stopped and the iteration
counter is cleared.
The ITERATION bit in US_CSR can be cleared by writing the Control Register with the RSTIT bit to 1.
Disable Successive Receive NACK
The receiver can limit the number of successive NACKs sent back to the remote transmitter. This is programmed by
setting the bit DSNACK in the US_MR. The maximum number of NACKs transmitted is programmed in the
MAX_ITERATION field. As soon as MAX_ITERATION is reached, the character is considered as correct, an
acknowledge is sent on the line and the ITERATION bit in the US_CSR is set.
setting the bit DSNACK in the US_MR. The maximum number of NACKs transmitted is programmed in the
MAX_ITERATION field. As soon as MAX_ITERATION is reached, the character is considered as correct, an
acknowledge is sent on the line and the ITERATION bit in the US_CSR is set.
D0
D1
D2
D3
D4
D5
D6
D7
RXD
Parity
Bit
Baud Rate
Clock
Start
Bit
Guard
Time 1
Next
Start
Start
Bit
Guard
Time 2
D0
D1
D2
D3
D4
D5
D6
D7
I/O
Parity
Bit
Baud Rate
Clock
Start
Bit
Guard
Time 1
Start
Bit
Guard
Time 2
D0
D1
Error
Repetition