AN2399

RFID library

17/22

Every time the RFID_Handler is invoked it powers the antenna with the 13.56 MHz carrier;

before exiting, it cuts-off the RF carrier.

8.2

SR176 commands layer

In order to manage the RFID tag, the CRX14 uses a set of commands. They are both used

to activate and select each device and to access (read/write or get 64 bits UID) the tag

EEPROM.

Here are all the functions used for reported RFID tags:

●

RF_ON();

// power on carrier frequency

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RF_OFF();

// power off carrier frequency

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Initiate(&RX_frame[0]);

// search a tag in the field

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Select (RFID_CHIPID,&RX_frame[0]);// activate a tag in the field

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Completion ( &RX_framebuf[0]);

// deselect tag

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Time_Read();

// program time for read

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ReadBlock (address, &RX_frame[ 0 ]);// read a word

●

Time_Write();

// program time for write

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WriteBlock (address, &TX_frame[ 0 ], &RX_frame[0]); // write a word

Each RF command has a dedicated 16-bit code (see SR176 and CRX14 datasheet). Tags

in the field recognize it and perform the required operation (activation, read, write,

deactivation, etc.).

RF Commands functions use CRX14 commands to access CRX14 registers. Basically each

RF command performs a write operation and a read operation to a CRX14 register.

8.3

CRX14 commands layer

This layer provides all functions needed to interface the STR710 microcontroller with the

CRX14 coupler device. CRX14 device uses 6 control registers to communicate both with the

Figure 8.

CRX14 control register access scheme

Depending on which register the user would like to access in read or write mode, several

functions are implemented.

I2C

CONTROL REGISTER

RF CIRCUITRY