MFRC522 datasheet(58/109 Pages) NXP

58 / 109 page

112132

Product data sheet

Rev. 3.2 — 22 May 2007

58 of 109

NXP Semiconductors

MFRC522

Contactless Reader IC

10.4.9 HS mode

In High-speed mode (HS mode) the device can transfer information at data rates of up to

3.4 Mbit/s, it remains fully downward compatible with Fast- or Standard mode (F/S mode)

for bi-directional communication in a mixed-speed bus system.

10.4.10 High Speed Transfer

To achieve a data rates of up to 3.4 Mbit/s the following improvements have been made to

the regular I2C-bus behavior.

• The inputs of the device in HS mode incorporates spike suppression and a

Schmitt-trigger at the SDA and SCL inputs with different timing constants compared to

F/S mode.

• The output buffers of the device in HS mode incorporates slope control of the falling

edges of the SDA and SCL signals with different fall time compared to F/S mode.

10.4.11 Serial Data transfer Format in HS mode

Serial data transfer format in HS mode meets the Standard mode I2C-bus specification.

HS mode can only commence after the following conditions (all of which are in F/S mode):

1. START condition (S)

2. 8-bit master code (00001XXX)

3. Not-acknowledge bit (A)

The active master then sends a repeated START condition (Sr) followed by a 7-bit slave

address with a R/W bit address, and receives an acknowledge bit (A) from the selected

MFRC522.

Data transfer continues in in Hs-mode after the next repeated START (Sr), and only

switches back to F/S-mode after a STOP condition (P). To reduce the overhead of the

master code, it's possible that a master links a number of Hs-mode transfers, separated

by repeated START conditions (Sr).

Fig 18. I2C HS mode protocol switch

MFRC522 Datasheet(PDF) 58 Page - NXP Semiconductors