Method for exchanging data between an automatic dispenser and a microcircuit card

A method of interchanging data between the non-volatile memory of a portable object and an automatic machine with which the portable object is temporarily coupled to enable goods or service to be delivered, the portable object storing in said non-volatile memory value information that can be debited by the machine in consideration for delivering the goods or service, and a ratification flag having two states, a ratified state and a non-ratified state, wherein the method comprises the successive following steps:

• a) the machine reads the state of the flag and jumps to step c) if said flag is in the non-ratified state;
• b) the machine issues to the portable object a command for debiting said value information by an amount corresponding to the goods or service to be delivered;
• c) the portable object:
• c1) records the debit by updating the value information, and
• c2) puts the flag into the non-ratified state,
• said sub-steps of recording the debit and putting the flag into the non-ratified state being performed in indivisible manner;
• d) the portable object issues to the machine an acknowledgement signal indicating that the debit has been recorded;
• c) the machine delivers the goods or service;
• f) the machine issues to the portable object a command for setting the flag to the ratified state;
• and
• g) the portable object puts the flag into the ratified state.