AN2646 datasheet(23/43 Pages) STMICROELECTRONICS

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AN2646 - Application note

ISO 7816-4 – smartcard commands

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variable-length record file contains records that may vary in length. As a result, variable-

length record files have a higher overhead in read/write access times as well as a higher

administrative overhead required by the file system.

A cyclic file allows applications to access records in a consistent and transparent manner. It

can be thought of as a ring of files. Write operations are performed on the next physical

record in the ring.

5.2.3

ISO 7816-4 functions

The few functions that are defined in ISO 7816-4 for selecting, reading and writing to files

will be briefly discussed below.

Select File

This command establishes a logical pointer to a particular file in the smartcard's file system.

This pointer is required for any file manipulation operation. Access to the smartcard's file

system is not multithreaded, however it is possible to have several file pointers defined at

any point in time. This is accomplished by the Manage Channel command, which

establishes multiple logical channels between the reader side application and the card. This

allows different files on the card to be in various states of access by the reader application at

the same time. The identification of the file can be provided in the following ways:

●

file identifier (2-byte value)

●

DF name (string of bytes)

●

path (concatenation of file identifiers)

●

short ID

Note that not all smartcards support all four naming mechanisms.

Read Binary

This command is used by the application on the reader side to retrieve a part of an EF on

the card. However, the EF must be a transparent file (not record-oriented). If the Read

Binary command is attempted on a record-oriented EF, the command will abort with an error

indicator being returned from the card.

The Read Binary command takes two parameters: an offset pointer from the start of the file

to the initial byte to be read, and the number of bytes to be read and returned to the reader.

Write Binary

This command is used to insert data into a transparent EF on the card. This command can

be used to set a series of bytes in the EF (that is set selected bits within a specified byte to a

value of1), clear a series of bytes or perform a write of a series of bytes in the EF.

Update Binary

A reader-side application can utilize this command to directly erase and store a contiguous

sequence of bytes in a transparent EF on the card. It effectively functions as a write

command that is a string of bytes provided in the command are written into the EF on the

card. The input parameters consist of an offset pointer from the start of the file as well as the

number of bytes to be written.

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