AN3255

Software description

Doc ID 17784 Rev 1

17/24

Figure 5.

Main application loop flowchart

During peripheral initialization, the application first configures the CR14 parameter register

to generate the 13,56 MHz RF field on the reader antenna.

Prior to issuing a Read/Write command (such as Get_UID()) to the memory tag, the tag

state machine must be put in the Selected state by sending a Select(Chip_ID) command. All

commands sent to the tag before this command is issued are ignored.

Once the peripheral initialization has completed, the application code enters a loop in which

it checks if a tag is present in the RF field by writing periodically the Initiate() command in

the CR14 Input/Output Frame register (see Appendix A: I2C memory addressing). If no tag

is present in the electromagnetic field, the STM8S105C6T6 enters the Active-halt power

saving mode for 512 ms and automatically wakes up to issue a new Initiate() command.

As soon as a tag is present in the electromagnetic field, it automatically enters the Ready

state in which its 8-bit random Chip_ID is initialized. When receiving the Initiate() command,

the tag then switches to the Inventory state in which its new 8-bit Chip_ID random value is

set and returned to the CR14. Since this application software does not implement the anti-