mfrc500 NXP Semiconductors, mfrc500 Datasheet - Page 91

• Manufacturer Part Number: mfrc500
• Description: Highly Integrated Iso14443a Reader Ic
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Highly Integrated ISO 14443A Reader IC
14.3.3 CORRELATION CIRCUITRY
The correlation circuitry calculates the degree of matching between the received and an expected signal.
The output is a measure for the amplitude of the expected signal in the received signal. This is done for both,
the Q- and the I-channel. The correlator delivers two outputs for each of the two input channels, resulting in
four output signals in total.
For optimum performance, the correlation circuitry needs the phase information for the signal coming from
the card. This information has to be defined by the µ-Processor by means of the register BitPhase[7:0]. This
value defines the phase relation between the transmitter and receiver clock in multiples of t
1/13.56 MHz.
14.3.4 EVALUATION AND DIGITIZER CIRCUITRY
For each bit-half of the Manchester coded signal the correlation results are evaluated. The evaluation and
digitizer circuit decides from the signal strengths of both bit-halves, whether the current bit is valid, and, if it is
valid, the value of the bit itself or whether the current bit-interval contains a collision.
To do this in an optimum way, the user may select the following levels:
•
•
After transmission of data, the card is not allowed to send its response before a certain time period, called
frame guard time in the standard ISO14443. The length of this time period after transmission shall be set in
the RxWait-Register. The RxWait-Register defines when the receiver is switched on after data transmission
to the card in multiples of one bit-duration.
If register bit RcvClkSelI is set to 1, the I-clock is used to clock the correlator and evaluation circuits. If set to
0, the Q-clock is used.
Note: It is recommended to use the Q-clock.
MinLevel: Defines the minimum signal strength of the stronger bit-half’s signal for being considered valid.
CollLevel: Defines the minimum signal strength that has to be exceeded by the weaker half-bit of the
Manchester-coded signal to generate a bit-collision. If the signal’s strength is below this value, a 1 and 0
can be determined unequivocally. CollLevel defines the minimum signal strength relative to the
amplitude of the stronger half-bit.
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Product Specification Rev. 3.2;December 2005
MF RC500
BitPhase
PUBLIC
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