AN2646 datasheet(22/43 Pages) STMICROELECTRONICS

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ISO 7816-4 – smartcard commands

AN2646 - Application note

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an error category and the other is used to specify a command-specific status or error

indication.

5.2.2

File system API

The file system is used on the non-volatile memory or EEPROM. It is defined as a simple

hierarchical structure (similar to conventional file systems). The file system may contain

three types of files (identified by a 2-byte identifier):

●

Master file (MF)

●

Dedicated file (DF)

●

Elementary file (EF)

There is one master file found on each smartcard and it is the root of the file system. A

master file may contain dedicated files or elementary files. The file identifier reserved for the

master file is 3F00. The directory file is essentially a container (or directory) for elementary

files - a DF may contain zero or more EFs. Dedicated files partition the smartcard into an

ordered structure of elementary files. A dedicated file must be given a unique file identifier

within the dedicated file or master file that contains it - allowing for a unique path for each

file. A dedicated file can also be referenced by name (1-16 bytes long). The naming

convention can be found in ISO 7816-5. An elementary file is a leaf node in the hierarchy

and contains the actual data. An elementary file can be identified by a 5-bit identifier within a

dedicated file. This file system hierarchy is illustrated in Figure 9.

Figure 9.

Smartcard file system architecture(1)

MF = master file, DF = dedicated file, EF = elementary file.

There are four types of elementary files:

●

Transparent file

●

Linear, fixed-length record file

●

Linear, variable-length record file

●

Cyclic, fixed-length record file

A transparent file is essentially a string of bytes, that is an unstructured binary file.

Consequently a byte offset from the start of the file is required when data is to be read or

written to this type of file. In addition, a command to read or write to a transparent file will

contain the length of the byte string to be read or written to the file.

Fixed- and variable-length files contain records that are identified by a sequence number. In

a fixed-length record file, all the records contain the same number of bytes. In contrast, a

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