Product data

MFRC631 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
Product data sheet
COMPANY PUBLIC
Rev. 3.3 — 4 February 2014
227433 20 of 120
NXP Semiconductors
MFRC631
High performance ISO/IEC 14443 A/B reader solution
8.4.4.3 I
2
C START and STOP conditions
To handle the data transfer on the I
2
C-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.
8.4.4.4 I
2
C byte format
Each byte has to be followed by an acknowledge bit. Data is transferred with the MSB
first, see Figure 15 “
START and STOP conditions”. The number of transmitted bytes
during one data transfer is unrestricted but shall fulfil the read/write cycle format.
Fig 14. Bit transfer on the I
2
C-bus.
001aam300
data line stable;
data valid
change
of data
allowed
SDA
SCL
Fig 15. START and STOP conditions
001aam301
START condition
S
SCL
SDA
SCL
SDA
STOP condition
P