Mif command group

With this command group, you can access MIFARE cards in low-level mode.

Whenever a card enters the HF field, it will be in idle state. From the idle state, a card switches to the requested state as soon as the Mif.Request command is executed. Cards in requested state participate in the anti-collision sequence, controlled by the Mif.Anticoll command, resulting in an unambiguous serial number belonging to one of the cards in the HF field. The card with this serial number may now be selected with the Mif.Select command. All other cards will fall back to idle state again and wait for the next call of the Mif.Request command. The selected card, however, changes from requested state to selected state.

When a card is in selected state, communication with the card is possible. Nevertheless, it is necessary to be authenticated before a sector of the card can be accessed. Authentication can be performed either with the Mif.AuthE2 command or with the Mif.AuthUser command. Both commands send a key to the currently selected card along with information regarding whether this key should be compared to key A or key B on the card. If the given key matches the corresponding sector's key (either key A or key B, as specified in the command's parameters), then access according to the access conditions of the desired sector will be granted.

Finally, a card that is in select state can be set to halt state. A card in halt state will not respond to any command unless a specially parameterized Mif.Request command is called, or when it leaves and then re-enters the HF field of the reader's antenna. The halt state is helpful when it is necessary to deal with multiple cards present in the reader's antenna HF field.

The Mif.Read and Mif.Write commands can be use to read/write data from/to a certain block. Additionally, a data sector may be turned into a special value sector (also called value block ), which is initialized with a specific starting value and can then only be changed by means of increment and decrement operations using the ChangeValue or ChangeValueBackup commands. Value sectors are very useful in some scenarios, such as for cash-based applications. To create a value sector, it is simply required to write specially formatted data to it:

• The first 4 bytes (bytes 0-3) represent the initially stored value.
• The following 4 bytes (bytes 4-7) have to be the two's complement of the first 4 bytes.
• The next 4 bytes (bytes 8-11) are a copy of the first 4 bytes.
• The last 4 bytes (bytes 12-15) contain the 1-byte address of a block which can be used for backup management. This address is stored on both byte 12 and byte 14, while its two's complement is stored on both byte 13 and byte 15. These 4 bytes are not affected by calls of the Mif.ChangeValue and Mif.ChangeValueBackup commands.

Each increment and decrement operation has to be followed by a transfer operation, using the Mif.TransferBlock command, in order to make the increment/decrement persistent. This feature guarantees that no data will be lost during a recalculation of the value on the card.