Abstract: Smart card readers dedicated to a particular application use both a microcontroller whose read only memory determines the running of the application, and a security component executing, under the control of the microcontroller, subroutines related to the security of the application (authentication, confidential programs, etc.). So that the manager of the application can have access to certain memory areas of the security component, provision is made for the microcontroller to be able to pass automatically to a so-called “transparent” mode, when a specific access code issued by a test card is recognized. In this mode, the read or write instructions for a memory area, issued by the test card, are interpreted by the microcontroller as being read or write instructions for a memory area of the security component rather than the microcontroller.