MFRC522_09 Datasheet, PDF (18/96 Pages) NXP Semiconductors – Contactless reader IC

NXP Semiconductors
MFRC522
Contactless reader IC
8.1.4.5 7-Bit addressing
During the I²C-bus address procedure, the first byte after the START condition is used to
determine which slave will be selected by the master.
Several address numbers are reserved. During device configuration, the designer must
ensure that collisions with these reserved addresses cannot occur. Check the I²C-bus
specification for a complete list of reserved addresses.
The I²C-bus address specification is dependent on the definition of pin EA. Immediately
after releasing pin NRSTPD or after a power-on reset, the device defines the I²C-bus
address according to pin EA.
If pin EA is set LOW, the upper 4 bits of the device bus address are reserved by
NXP Semiconductors and set to 0101b for all MFRC522 devices. The remaining 3 bits
(ADR_0, ADR_1, ADR_2) of the slave address can be freely configured by the customer
to prevent collisions with other I²C-bus devices.
If pin EA is set HIGH, ADR_0 to ADR_5 can be completely specified at the external pins
according to Table 5 on page 8. ADR_6 is always set to logic 0.
In both modes, the external address coding is latched immediately after releasing the
reset condition. Further changes at the used pins are not taken into consideration.
Depending on the external wiring, the I²C-bus address pins can be used for test signal
outputs.
MSB
LSB
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
R/W
slave address
Fig 16. First byte following the START procedure
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8.1.4.6 Register write access
To write data from the host controller using the I²C-bus to a specific register in the
MFRC522 the following frame format must be used.
• The first byte of a frame indicates the device address according to the I²C-bus rules.
• The second byte indicates the register address followed by up to n-data bytes.
In one frame all data bytes are written to the same register address. This enables fast
FIFO buffer access. The Read/Write (R/W) bit is set to logic 0.
MFRC522_33
Product data sheet
PUBLIC
Rev. 3 — 26 October 2009
112133
© NXP B.V. 2009. All rights reserved.
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