Atmel Evaluation Kit AT91SAM9G25-EK AT91SAM9G25-EK Data Sheet
Product codes
AT91SAM9G25-EK
798
SAM9G25 [DATASHEET]
11032C–ATARM–25-Jan-13
Figure 39-29.Connection of a Smart Card to the USART
When operating in ISO7816, either in T = 0 or T = 1 modes, the character format is fixed. The configuration is 8 data bits,
even parity and 1 or 2 stop bits, regardless of the values programmed in the CHRL, MODE9, PAR and CHMODE fields.
MSBF can be used to transmit LSB or MSB first. Parity Bit (PAR) can be used to transmit in normal or inverse mode.
Refer to
even parity and 1 or 2 stop bits, regardless of the values programmed in the CHRL, MODE9, PAR and CHMODE fields.
MSBF can be used to transmit LSB or MSB first. Parity Bit (PAR) can be used to transmit in normal or inverse mode.
Refer to
The USART cannot operate concurrently in both receiver and transmitter modes as the communication is unidirectional
at a time. It has to be configured according to the required mode by enabling or disabling either the 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.
at a time. It has to be configured according to the required mode by enabling or disabling either the 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.
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.
I/O line at their negative value.
39.7.4.2 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.
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
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
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.
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.
Register (US_RHR). It appropriately sets the PARE bit in the Status Register (US_SR) so that the software can handle
the error.
Figure 39-30.T = 0 Protocol without Parity Error
Figure 39-31.T = 0 Protocol with Parity Error
Smart
Card
SCK
CLK
TXD
I/O
USART
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