CR14 datasheet(23/46 Pages) STMICROELECTRONICS

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CR14

5 Applying the I²C protocol to the CR14 registers

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5.2

I²C Input/Output Frame Register Protocol

Figure 13 shows how to store a PICC request frame command of N Bytes into the Input/Output

Frame Register.

After the I²C STOP condition, the request frame is RF transmitted in the ISO14443 type-B

format. The CR14 then waits for the PICC answer frame which will also be stored in the Input/

Output Frame Register. The request frame is over-written by the answer frame.

Figure 14 shows how to read an N-Byte PICC answer frame.

The two CRC Bytes generated by the PICC are not stored.

The CR14 continues to output data Bytes until a NoACK has been generated by the I²C Host,

and received by the CR14. After all 36 Bytes have been output, the CR14 “rolls over”, and

starts outputting from the start of the Input/Output Frame Register again.

The CR14 supports the I²C Current Address and Random Address Read modes. The Current

Address Read mode can be used if the previous command was issued to the register where the

Read is to take place.

Figure 13. Host-to-CR14 Transfer: I²C Write to Input/Output Frame Register for ISO14443B

Figure 14. CR14-to-Host Transfer: I²C Random Address Read from Input/Output Frame

1 0 1 0 XX X

01h

ACK

Request Frame

Length N

Input/Output

Address

Device

Select

Code

Bus

Master

CR14

Write

Bus

Slave

ai12041

R/W

Data 1

Data 2

PICC

Command

Parameter

PICC

Command

Code

Data N

PICC

Command

Parameter

PICC

Command

Parameter

ACK

10 10 XXX

01h

ACK

Received

Frame

Length

Input/Output

Address

Device

Select

Code

Bus

Master

CR14

Read

Bus

Slave

ai12042

R/W

Data1

Data 2

Answer

Frame

Data

Answer

Frame

Data

Data N

Answer

Frame

Data

Answer

Frame

Data

NoACK

ACK

1 0 1 0 XXX

Device

Select

Code

R/W

ACK

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