CR14 Datasheet, PDF (31/46 Pages) STMicroelectronics – Low Cost ISO14443 type-B Contactless Coupler Chip with Anti-Collision and CRC Management

CR14
7 Tag access using the CR14 coupler
7 Tag access using the CR14 coupler
In all the following I²C commands, the last three bits of the Device Select Code can be replaced
by any of the three-bit binary values (000, 001, 010, 011, 100, 101, 110, 111). These values are
linked to the logic levels applied to the E2, E1 and E0 pads of the CR14.
7.1 Standard TAG Command Access Description
Standard PICC commands, like Read and Write, are generated by the CR14 using the Input/
Output Frame Register.
When the host needs to send a standard frame command to the PICC, it first has to internally
generate the complete frame, with the command code followed by the command parameters.
Only the two CRC Bytes should not be generated, as the CR14 automatically adds them during
the RF transmission.
When the frame is ready, the host has to write the request frame into the Input/Output Frame
Register using the I²C write command specified in Figure 13 on page 23. After the I²C STOP
condition, the CR14 inserts the I²C Bytes in the required ISO character format ( Figure 20) and
starts to transmit the request frame to the PICC. Once the RF transmission is over, the CR14
waits for the PICC to send an answer frame.
If the PICC answers, the characters received (Figure 26) are demodulated, decoded and stored
into the Input/Output Frame Register, as specified in Table 4. During the entire RF
transmission, the CR14 disconnects itself from the I²C bus. On reception of the PICC EOF, the
CR14 checks the CRC and reconnects itself to the I²C bus.
The host can then get the PICC answer frame by issuing an Input/Output Frame Register Read
on the I²C bus, as specified in Figures 14 and 15.
If no answer from the PICC is detected after a time-out delay, fixed in the Parameter Register
(bits b₅ and b₆), the Input/Output Frame Register is set as specified in Table 4.
Figure 28. Standard TAG Command: Request Frame Transmission
S
T
A
R
T
Device
Select
Code
I²C
Input/
Output
Register
Address
Request
Frame
Length
01h
N
TAG
Cmd
Code
Param
Param
Data 1 Data 2 Data
S
Param
T
O
P
Data N
CR14
SOF
TAG
Cmd
Code
Param
Param
Param
CRC
CRC
SR14
EOF
RF
SOF
Data 1 Data 2
Data
Data N
CRC
CRC
EOF
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