STW4811M STMicroelectronics, STW4811M Datasheet - Page 20

• Manufacturer Part Number: STW4811M
• Description: Power Management For Multimedia Processors
• Manufacturer: STMicroelectronics

Functional description
4.2.4
Note:
20/87
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
(
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.
Both I2C are configured as slave serial interface compatible with I2C registered trademark
of Phillips Inc. (version 2.1).
I2C interface description
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):
●
●
It is composed of:
●
●
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).
●
●
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.
Table 23
SCL / USBSCL: input clock used to shift data
SDA / USBSDA: input/output bidirectional data transfers
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
Device ID in write mode: 5Ah (01011010)
Device ID in read mode: 5Bh (01011011)
USBSDA
USBSCL
). I2C interface is used to read status information from inside the device.
SDA
SCL
I2C interface block diagram
SCL or USBSCL
SDA or USBSDA
usb_i2c_ctrl
SDA
SCL
USB registers
Main registers
STw4811M/STw4811N