Thu Jul 11 10:24:56 EDT 2013

AT91SAM7 ISO7816 mode

AT91SAM7S256 data sheet:   Baud Rate in ISO 7816 Mode
29.6.4     ISO7816 Mode

US_MR:USART_MODE = 0x4 for protocol T = 0 
TXD becomes bidirectional

The USART cannot operate concurrently in both receiver and transmitter
modes as the com- munication 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.

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. The USART does not support this format and the user
has to perform an exclusive OR on the data before writing it in the
Trans- mit Holding Register (US_THR) or after reading it in the
Receive Holding Register (US_RHR).

-> TS = 3B / 3F (direct / inverse)