Atmel Xplained Pro Evaluation Kit ATSAM4E-XPRO ATSAM4E-XPRO Fiche De Données
Codes de produits
ATSAM4E-XPRO
909
SAM4E [DATASHEET]
Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14
receiver or the transmitter as desired. Enabling both the receiver and the transmitter at the same time in ISO7816
mode may lead to unpredictable results.
mode may lead to unpredictable results.
The ISO7816 specification defines an inverse transmission format. Data bits of the character must be transmitted
on the I/O line at their negative value.
on the I/O line at their negative value.
38.7.4.2 Protocol T = 0
In T = 0 protocol, a character is made up of one start bit, eight data bits, one parity bit and one guard time, which
lasts two bit times. The transmitter shifts out the bits and does not drive the I/O line during the guard time.
lasts two bit times. The transmitter shifts out the bits and does not drive the I/O line during the guard time.
If no parity error is detected, the I/O line remains to 1 during the guard time and the transmitter can continue with
the transmission of the next character, as shown in
the transmission of the next character, as shown in
.
If a parity error is detected by the receiver, it drives the I/O line to 0 during the guard time, as shown in
. This error bit is also named NACK, for Non Acknowledge. In this case, 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 register (US_SR) so that the software
can handle the error.
Holding register (US_RHR). It appropriately sets the PARE bit in the Status register (US_SR) so that the software
can handle the error.
Figure 38-31. T = 0 Protocol without Parity Error
Figure 38-32. 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.
register. 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 US_MR. If
INACK is to 1, no error signal is driven on the I/O line even if a parity bit is detected.
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.
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.
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