at91sam9263 ATMEL Corporation, at91sam9263 Datasheet - Page 528

• Manufacturer Part Number: at91sam9263
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

Figure 33-21. T = 0 Protocol without Parity Error
Figure 33-22. T = 0 Protocol with Parity Error
33.6.4.3
33.6.4.4
33.6.4.5
6249D–ATARM–20-Dec-07
Baud Rate
Baud Rate
Clock
I/O
Clock
RXD
Receive Error Counter
Receive NACK Inhibit
Transmit Character Repetition
Start
Bit
Start
Bit
D0
If a parity error is detected by the receiver, it drives the I/O line at 0 during the guard time, as
shown in
the character lasts 1 bit time more, as the guard time length is the same and is added to the
error bit time which lasts 1 bit time.
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 Reg-
ister (US_SR) so that the software can handle the error.
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 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.
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.
D0
D1
D1
Figure
D2
D2
33-22. This error bit is also named NACK, for Non Acknowledge. In this case,
D3
D3
D4
D4
D5
D5
D6
D6
D7
AT91SAM9263 Preliminary
D7
Parity
Bit
Parity
Bit
Time 1
Guard
Time 1
Guard
Error
Time 2
Guard
Time 2
Guard
Start
Next
Bit
Start
Bit
Repetition
D0
D1
528