MFRC522 datasheet(22/96 Pages) NXP

22 / 96 page

MFRC522_33

Product data sheet

PUBLIC

Rev. 3 — 26 October 2009

112133

22 of 96

NXP Semiconductors

MFRC522

Contactless reader IC

8.1.4.11

Switching between F/S mode and HS mode

After reset and initialization, the MFRC522 is in Fast mode (which is in effect F/S mode as

Fast mode is downward-compatible with Standard mode). The connected MFRC522

recognizes the “S 00001XXX A” sequence and switches its internal circuitry from the Fast

mode setting to the HS mode setting.

The following actions are taken:

1. Adapt the SDA and SCL input ﬁlters according to the spike suppression requirement

in HS mode.

2. Adapt the slope control of the SDA output stages.

It is possible for system conﬁgurations that do not have other I2C-bus devices involved in

the communication to switch to HS mode permanently. This is implemented by setting

Status2Reg register’s I2CForceHS bit to logic 1. In permanent HS mode, the master code

is not required to be sent. This is not deﬁned in the speciﬁcation and must only be used

when no other devices are connected on the bus. In addition, spikes on the I2C-bus lines

must be avoided because of the reduced spike suppression.

8.1.4.12

MFRC522 at lower speed modes

MFRC522 is fully downward-compatible and can be connected to an F/S mode I2C-bus

system. The device stays in F/S mode and communicates at F/S mode speeds because a

master code is not transmitted in this conﬁguration.

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