RFID library

AN2399

16/22

8.1.4

RFID communication status report

The communication status can be checked using the RFID_Handler return parameter. It

returns:

●

Presence/absence of tag into the space covered from magnetic field.

●

Error on reading/writing RFID EEPROM

●

Error getting 64 bits UID

●

Error on cut-off RF carrier.

In order to access an RFID EEPROM, the application layer function has to implement a

Finite State Machine (FSM) as depicted in the following picture:

Figure 7.

RFID: state transition diagram

When invoking the application layer, FSM searches for a tag (for a period of time specified in

RFID_Polling_timeout); when a tag device is found, the FSM attempts to recover the tag

CHIP_ID using the “Initiate()” command. If the tag responds with its own CHIP_ID the FSM

attempts to select it in order to perform actions according the RFID_Action parameter.

The FSM performs these actions using the “init_RFID()”. It describes all states from

POWER OFF to SELECTED.

When selected, the application layer FSM uses three functions to perform the requested

actions:

●

GetSR176_64UID(&RFID_UID[0]);

●

ReadSR176_EEPROM(&RX_frame[0],RX_offset,RX_lenght);

●

WriteSR176_EEPROM(&TX_frame[0],TX_offset,TX_lenght);

When all requested actions are performed, the FSM deselects the tag device via a

“Completion()” command.

POWER-OFF

READY

ACTIVE

SELECTED

DEACTIVATED

DESELECTED

SELECT(Chip_ID)

Out of

Field

Out of

Field

In Field

INITIATE()

Out of

Field

SELECT(Chip_ID)

COMPLETION

Out of

Field

SELECT(

≠Chip_ID)

SELECT(Chip_ID)

READ_BLOCK()

WRITE_BLOCK()

PROTECT_BLOCK()

GET_PROTECTION()