AN3255 datasheet(8/24 Pages) STMICROELECTRONICS

8 / 24 page

Application description

AN3255

8/24

Doc ID 17784 Rev 1

Figure 2.

Ack Polling flowchart

1.2.3

Reader-tag protocol

Standard tag commands such as Read and Write are generated by the CR14 using its

Input/Output Frame register. To send a command to the tag, the STM8S105C6 host first

generates internally the complete frame containing the command code followed by the

command parameters (if required). Only the 2 CRC bytes must not be generated as the

CR14 automatically adds them during the RF transmission.

Once the frame is ready, the host writes it into the Input/Output Frame register using an I2C

Write command.

If the tag answers, the characters received are demodulated, decoded and stored into the

input/output frame buffer. During the entire RF transmission, the CR14 disconnects itself

from the I2C bus. On reception of the tag EOF, the CR14 checks the CRC and reconnects to

the I2C bus. The host can then get the tag answer frame by issuing an Input/Output Frame

Refer to the CR14 datasheet for details on Read and Write commands.

1.2.4

Commands and tag states

The tag can be switched into different states (see Figure 3). The tag only answers specific

commands depending on its current state. These states are specified by the ISO 15693

standard. For details concerning these states, refers to one of ST short range contactless

EEPROM datasheet (for example SRI2K) available from http://www.st.com.

AN3255 Datasheet(PDF) 8 Page - STMicroelectronics