CR14 datasheet(32/46 Pages) STMICROELECTRONICS

32 / 46 page

7 Tag access using the CR14 coupler

CR14

32/46

Figure 29. Standard TAG Command: Answer Frame Reception

Figure 30. Standard TAG Command: Complete TAG Access Description

7.2

Anti-Collision TAG Sequence

The CR14 can identify an ST short range memory using a proprietary anti-collision system.

Issuing an I²C Write command to the Slot Marker Register (Figure 16) causes the CR14 TO

automatically generate a 16-slot anti-collision sequence, and to store the identified Chip_ID in

the Input/Output Frame Register, as specified in Table 5.

After receiving the Slot Marker Register I²C Write command, the CR14 generates an RF

PCALL16 command followed by fifteen SLOT_MARKER commands, from SLOT_MARKER(1)

to SLOT_MARKER(15). After each command, the CR14 waits for a tag answer. If the answer is

correctly decoded, the corresponding Chip_ID is stored in the Input/Output Frame Register. If

there is no answer, or if the answer is wrong (with a CRC error, for example), the CR14 stores

an error code in the Input/Output Frame Register. At the end of the sequence, the host has to

read the Input/Output Frame Register to retrieve all the identified Chip_IDs.

Device

Select

Code

Input/

Output

Address

Answer

Frame

Length

TAG

Data

SOF

EOF

Data 1

Data

Data 2

Data P

CRC

TAG

SOF

TAG

Data

TAG

Data

TAG

Data

TAG

Data

TAG

EOF

TAG

CRC

TAG

CRC

I²C

ai09261

Data 1

Data

Data 2

Data P

01h

TAG

Data

TAG

Data

TAG

Data

Device

Select

Code

Write

I/O

Address

Request

Frame

Length

Request

Frame

Bytes

I²C

START

STOP

CRC

Request

Frame

Characters

SOF

EOF

CRC

TAG

Answer Frame

Characters

SOF

EOF

<-->

Device

Select

Code

Read

Answer

Frame

Length

Request

Frame

Bytes

START

STOP

ai09262

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