MFRC522 datasheet(53/109 Pages) NXP

53 / 109 page

112132

Product data sheet

Rev. 3.2 — 22 May 2007

53 of 109

NXP Semiconductors

MFRC522

Contactless Reader IC

10.4.2 Data validity

Data on the SDA line shall be stable during the HIGH period of the clock. The HIGH or

LOW state of the data line shall only change when the clock signal on SCL is LOW.

10.4.3 START and STOP conditions

To handle the data transfer on the I2C-bus, unique START (S) and STOP (P) conditions

are defined.

A START condition is defined with a HIGH to LOW transition on the SDA line while SCL is

HIGH.

A STOP condition is defined with a LOW to HIGH transition on the SDA line while SCL is

HIGH.

The master always generates the START and STOP conditions. The bus is considered to

be busy after the START condition. The bus is considered to be free again a certain time

after the STOP condition.

The bus stays busy if a repeated START (Sr) is generated instead of a STOP condition. In

this respect, the START (S) and repeated START (Sr) conditions are functionally identical.

Therefore, the S symbol will be used as a generic term to represent both the START and

repeated START (Sr) conditions.

Fig 12. Bit transfer on the I2C-bus.

Fig 13. START and STOP conditions.

MFRC522 Datasheet(PDF) 53 Page - NXP Semiconductors