Data Sheet

Product data sheet

COMPANY PUBLIC

Rev. 3.9 — 27 April 2016

112139 35 of 95

NXP Semiconductors

MFRC522

Standard performance MIFARE and NTAG frontend

9. MFRC522 registers

9.1 Register bit behavior

Depending on the functionality of a register, the access conditions to the register can vary.

In principle, bits with same behavior are grouped in common registers. The access

conditions are described in Table 19

Table 19. Behavior of register bits and their designation

Abbreviation Behavior Description

R/W read and write These bits can be written and read by the microcontroller. Since

they are used only for control purposes, their content is not

influenced by internal state machines, for example the

ComIEnReg register can be written and read by the

microcontroller. It will also be read by internal state machines but

never changed by them.

D dynamic These bits can be written and read by the microcontroller.

Nevertheless, they can also be written automatically by internal

state machines, for example the CommandReg register changes

its value automatically after the execution of the command.

R read only These register bits hold values which are determined by internal

states only, for example the CRCReady bit cannot be written

externally but shows internal states.

W write only Reading these register bits always returns zero.

reserved - These registers are reserved for future use and must not be

changed. In case of a write access, it is recommended to always

write the value “0”.

RFT - These register bits are reserved for future use or are for

production tests and must not be changed.