STW4811MBHDSLASHLF datasheet(21/86 Pages) STMICROELECTRONICS

21 / 86 page

Functional description

STw4811M/STw4811N

20/85

4.2.4

I2C Interface

The device supports two I2C bus interfaces. One main interface (SDA,SCL) controls power

management and all programmable functions, the second interface (USBSDA, USBSCL) is

dedicated to USB control. STw4811 allows to work with only the main I2C interface to

control all the functions, including the USB, via ‘usb_i2c_ctrl’ bit of

power control register

(

Table 23). I2C interface is used to read status information from inside the device.

Flags, interrupt and write registers are used to configure the device functions (threshold,

clock division, output voltage, etc....). By default, the main I2C interface (SCL,SDA) controls

the main registers and USB I2C interface (USBSCL, USBSDA) controls

USB registers.

Figure 6.

I2C interface block diagram

Both I2C are configured as slave serial interface compatible with I2C registered trademark

of Phillips Inc. (version 2.1).

I2C interface description

Note:

When not using the USB I2C interface, the two pins USBSCL and USCSDA must be

connected to the VIO voltage.

STw4811 I2C is a slave serial interface with a serial data line (SDA or USBSDA) and a serial

clock line (SCL or USBSCL):

●

SCL / USBSCL: input clock used to shift data

●

SDA / USBSDA: input/output bidirectional data transfers

It is composed of:

●

One filter to reject spikes on the bus data line and preserve data integrity

●

Bidirectional data transfers up to 400kbit/s (fast mode) via SDA or USBSDA signal

The SDA or USBSDA signal contains the input/output control and data signals that are

shifted in the device, MSB first. The first bit must be high (START) followed by the Device ID

(7 bits) and Read/Write bit control (1 indicates read access, a logical 0 indicates a write

access).

●

Device ID in write mode: 5Ah (01011010)

●

Device ID in read mode: 5Bh (01011011)

Then STw4811 sends an acknowledge at the end of an 8 bit transfer. The next 8 bits

correspond to the register address followed by another acknowledge. The 8-bit data field is

sent last, followed by a last acknowledge.

Main registers

SDA

USBSCL

SCL

SDA or USBSDA

SCL or USBSCL

USBSDA

USB registers

SDA

SCL

usb_i2c_ctrl

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