Selects a Dedicated File (DF) on the (U)SIM, so Elementary Files (EFs) that are to be accessed by command +CRSM can be uniquely identified. The +CRSM command only takes EF as parameter and, since EFs in different DFs can have the same file ID, certain files are not accessible with +CRSM alone.

A DF can be seen as a "directory" and *ECDF could be regarded as a "change directory" command. Note: *ECDF has impact on the standard behaviour of +CRSM: AT+CRSM does not specify how files in different DFs will be accessed, but the introduction of *ECDF imposes the restriction that only EFs in the currently selected DF may be accessed with +CRSM. Even if an EF can be uniquely identified throughout all DFs, it is required that *ECDF has selected the correct DF for the EF to be accessed.

Use AT command in a programming environment

With ActiveXperts Serial Port Component (an ActiveXperts product), you can integrate AT modem communications in scripts, console applications, GUI form applications, web applications and web services.

With ActiveXperts SMS Component (an ActiveXperts product), you can also integrate AT modem communications in an environment that has many aspects of GSM modem communications implemented in interface functions.