AN2399 datasheet(12/22 Pages) STMICROELECTRONICS

номер детали	AN2399

подробное описание детали	RFID library for SR176 tag management with STR71x

PDF	22 Pages

Scroll/Zoom	100%

производитель	STMICROELECTRONICS [STMicroelectronics]

домашняя страница	http://www.st.com

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12 / 22 page

Overview of RFID reader using STR710

AN2399

12/22

7.2

Interfacing with STR7xx using I2C peripheral

Due to the fact that the STR7xx microcontroller has a 3.3 voltage supply and the CRX14

device work at 5 V, a level shifter has to be inserted on the I2C bus in order to adjust the

voltage levels.

Figure 4.

Interfacing the I2C bus from 3.3 V to 5 V

The I2C Bus Interface on STR71x provides both multimaster and slave functions, and

controls all I2C bus-specific sequencing, protocol, arbitration and timing. It also supports fast

I2C mode (400 kHz).

For the purpose of this application note, the I2C peripheral works as Master

transmitter/receiver. In Master mode, it initiates a data transfer and generates the clock

signal. A serial data transfer always begins with a start condition and ends with a stop

condition. Both start and stop conditions are generated in master mode by hardware as

soon as the Master mode is selected.

Data and addresses are transferred as 8-bit bytes, MSB first. The first byte(s) following the

start condition contain the address (one in 7-bit mode, two in 10-bit mode).

A 9th clock pulse follows the 8 clock cycles of a byte transfer, during which the receiver must

send an acknowledge bit to the transmitter. Refer to Figure 5.

Figure 5.

I2C bus protocol

SDA

SCL

MSB

ACK

START

CONDITION

STOP

CONDITION

AN2399 датащи(PDF) 12 Page - STMicroelectronics