CRX14 Tag access using the CRX14 coupler
Doc ID 8880 Rev 4 31/47
7 Tag access using the CRX14 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 CRX14.
7.1 Standard TAG command access description
Standard PICC commands, like Read and Write, are generated by the CRX14 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 CRX14 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 CRX14 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
CRX14 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 Ta ble 4 . During the entire RF
transmission, the CRX14 disconnects itself from the I²C bus. On reception of the PICC EOF,
the CRX14 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 b
5
and b
6
), the Input/Output Frame Register is set as specified in Tab le 4.
Figure 28. Standard TAG command: request frame transmission
S
T
A
R
T
Device
Select
Code
Input/
Output
Register
Address
Request
Frame
Length
TAG
Cmd
Code
Param Param Param
S
T
O
P
SOF EOFData 1 DataData 2 Data N CRC CRC
CRX14
SOF
TAG
Cmd
Code
Param Param Param
SRX14
EOF
CRC CRC
I²C
RF
ai09260
Data 1 DataData 2 Data N01h N
