20.4.2.4.1 Protocol and Frame Details

The smart card communication scheme is based on an Elementary Time Unit (ETU) that is also the bit clock. The smart card will provide the ETU value in the ATR, and the terminal is configured accordingly. A character frame consists of ten bits, a Start bit, eight data bits and a Parity bit. Depending on the mode, guard and wait times are used to separate bytes and message transitions.

The ISO 7816 specification defines two communication logic conventions: direct and inverse. Direct convention is defined as LSB first and a high state as logic one. Inverse mode is defined as MSB first, and a low on the line is interpreted as a logic high. The logic convention is set using the CONV bit (UxSCCON[3]).