MFRC522 datasheet(60/109 Pages) NXP

60 / 109 page

112132

Product data sheet

Rev. 3.2 — 22 May 2007

60 of 109

NXP Semiconductors

MFRC522

Contactless Reader IC

10.4.12 Switching from F/S to HS mode and Vice Versa

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

Fast mode is downward compatible to 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.

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.

For system configurations, where no other I2C devices are involved in the communication,

have an additional possibility to switch to HS-mode. By setting the bit I2CForceHS in

the HS-mode permanent meaning that sending the master code is no longer necessary.

This is not according the specification and should only be used when no other devices are

connected on the bus. Spikes on the I2C lines shall be avoided because of the reduced

spike suppression.

10.4.13 MFRC522 at Lower Speed modes

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

system. As no master code will be transmitted in such a configuration, the device stays in

F/S mode and communicates at F/S mode speeds.

MFRC522 Datasheet(PDF) 60 Page - NXP Semiconductors