mfrc531 NXP Semiconductors, mfrc531 Datasheet - Page 79

• Manufacturer Part Number: mfrc531
• Description: Iso/iec 14443 Reader Ic
• Manufacturer: NXP Semiconductors

NXP Semiconductors
MFRC531_34
Product data sheet
PUBLIC
11.2.2.1 Using the Receive command
11.2.2.2 RF channel redundancy and framing
11.2.2 Receive command 16h
Figure 17
status is checked. This leads to FIFO empty state being held LOW which keeps the
accept further data active. The new byte written to the FIFO buffer is transmitted using the
RF interface.
Accept further data is only changed by the check FIFO empty function. This function
verifies FIFO empty for one bit duration before the last expected bit transmission.
Table 133. Transmission of frames of more than 64 bytes
Table 134. Receive command 16h
The Receive command activates the receiver circuitry. All data received from the RF
interface is written to the FIFO buffer. The Receive command can be started either using
the microprocessor or automatically during execution of the Transceive command.
Remark: This command can only be used for test purposes since there is no timing
relationship to the Transmit command.
After starting the Receive command, the internal state machine decrements to the RxWait
register value on every bit-clock. The analog receiver circuitry is prepared and activated
from 3 down to 1. When the counter reaches 0, the receiver starts monitoring the incoming
signal at the RF interface.
When the signal strength reaches a level higher than the RxThreshold register
MinLevel[3:0] bits value, it starts decoding. The decoder stops when the signal can no
longer be detected on the receiver input pin RX. The decoder sets bit RxIRq indicating
receive termination.
The different phases of the receive sequence are monitored using the PrimaryStatus
register ModemState[2:0] bits; see
Remark: Since the counter values from 3 to 0 are needed to initialize the analog receiver
circuitry, the minimum value for RxWait[7:0] is 3.
The decoder expects the SOF pattern at the beginning of each data stream. When the
SOF is detected, it activates the serial-to-parallel converter and gathers the incoming data
bits. Every completed byte is forwarded to the FIFO buffer.
Frame definition
8-bit with parity
8-bit without parity
x-bit without parity
Command
Receive
also shows write access to the FIFOData register just before the FIFO buffer’s
Value
16h
Rev. 3.4 — 26 January 2010
Action
activates receiver circuitry
056634
Section 11.2.4 on page
Verification at:
8
7
(x − 1)
th
th
bit
bit
th
bit
82.
ISO/IEC 14443 reader IC
Arguments
and data
-
MFRC531
© NXP B.V. 2010. All rights reserved.
Returned
data
data stream
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