Datasheet

449
SAM9261 [DATASHEET]
Atmel-6062O-ATARM-SAM9261-Datasheet_21-Jun-16
Figure 31-21. T = 0 Protocol without Parity Error
Figure 31-22. T = 0 Protocol with Parity Error
31.6.4.3 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.
31.6.4.4 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 at 1, no error signal is driven on the I/O line even if a parity bit is detected, but the
INACK bit is set in the Status Register (US_SR). The INACK bit can be cleared by writing the Control Register
(US_CR) with the RSTNACK bit at 1.
Moreover, if INACK is set, the erroneous received character is stored in the Receive Holding Register, as if no
error occurred. However, the RXRDY bit does not raise.
31.6.4.5 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 Mode Register
(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.
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.
The ITERATION bit in US_CSR can be cleared by writing the Control Register with the RSIT bit at 1.
31.6.4.6 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 Mode Register (US_MR). The maximum number of NACK 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 Channel Status Register is set.
D0
D1
D2
D3
D4
D5 D6 D7
RXD
Parity
Bit
Baud Rate
Clock
Start
Bit
Guard
Time 1
Next
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