RFID - Elektor

9 Elektor RFID Projects
tion. The received data bytes are automatically written to the FIFO buffer by the contactless
UART. Because only one FIFO is available for both reading and writing, the card
command is overwritten. Since all communication is based on the master-slave principle,
overwriting the command data presents no problems. The entire procedure for contactless
communication is controlled solely by the MF RC522’s control, configuration and
status registers.
9.1.1 Elektor RFID Reader Library: MF RC522
The RC522.ReadSFR() and RC522.WriteSFR() methods in the Elektor RFID Reader
library enable direct access to the MF RC522 registers. In this case, the reader firmware’s
function is reduced to that of a special USB-to-I2C converter for controlling the
MF RC522 UART.
Table 9.1. Methods available for direct control of the MF RC522 SFRs.
Method
byte ReadSFR(byte
sfrAddr);
void WriteSFR(byte
sfrAddr, byte sfrValue)
Description
Returns the value of the given MF RC522 special
function register (SFR).
Writes the sfrValue parameter to the given
MF RC522 SFR.
With the help of these two methods, it is possible to develop and test parts of the reader
firmware directly on the PC. This eliminates time-consuming microcontroller programming
(flashing). All of the reader IC’s analog parameters can be changed by configuring the
corresponding SFR. Tuning the antenna and optimizing the reader’s range requires repeated
changing of the MF RC522’s analog parameters, and thus the repeated updating
of the corresponding register values. Using the conventional approach, the firmware would
have to be updated for every new iteration. It is much more efficient in this case to adjust
the register values using a PC program (e.g. a Smart Card Magic.Net script) and then
perform the RF measurements. It’s only necessary to load a modified version of the reader
firmware into flash memory after successful analog performance optimization.
copyright Elektor
9.1.2 Program Examples
9.1.2.1 Changing the RF Parameter Configuration
This example shows how one overwrites the modulator and demodulator default values,
for test purposes. The default values are automatically restored from the reader firmware
when power is supplied to the RFID Reader.
Note
The MF RC522 offers the possibility of connecting different antenna configurations.
Therefore, you should not change the Elektor RFID Reader
MF RC522 SFRs that define the output driver circuit. Otherwise, in extreme
cases, this could lead to a short circuit that could destroy the
reader IC or other circuit components.
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