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AN2533 Application note
STw481x register access, how to use STw481x indirect addressed registers
Introduction
STw481x applies to STw4810, STw4811N and STw4811M part numbers. This document provides some guidance to access STw481x I2C registers and STw481x indirect addressed registers. The two I2C interfaces, main I2C and USB I2C, are described, as well as the procedure to read and write indirect addressed registers.
October 2007
Rev 1
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Registers access
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Registers access
STw481x uses industry standard I2C bus for registers access. The device supports two I2C bus interfaces. The main interface (SDA,SCL) controls the power management and all the programmable functions. The USB interface (USBSDA, USBSCL) is dedicated to USB control. STw481x allows to work only with the main I2C interface to control all the functions including the USB, via `usb_i2c_ctrl' bit of power control register (bit 0 in power control register at address 06h). The device ID is 5Ah (01011010) in read mode and 5Bh (01011011) in write mode.
Code conventions
Assuming that STw481x I2C registers are accessed through the following software functions: void STw481x_main_I2C_write(unsigned char address, unsigned char data); unsigned char STw481x_main_I2C_read(unsigned char address); void STw481x_USB_I2C_write(unsigned char address, unsigned char data); unsigned char STw481x_USB_I2C_read(unsigned char address); Table 1. STw481x registers
Description USB registers Configuration 1 register Reserved Power control registers used for indirect addressing Configuration 1 register Vcore_sleep register Main I2C Main I2C Main I2C I2C control Main I2C or USB I2C Main I2C
Address 00h to 10h 11h 12h to 1Dh 1Eh and 1Fh 20h 21h
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Power management registers (main I2C)
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Power management registers (main I2C)
Registers at addresses 11h, 20h and 21h are dedicated to power management and control. Those registers are directly accessed by I2C bus. Registers 1Eh and 1Fh used for indirect addressing are also accessed by the main I2C bus.
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Power control registers with indirect addressing
The 4-bit wide internal registers are accessed by indirect addressing using registers 1Eh and 1Fh registers from the main I2C bus. For indirect addressing using 1Eh and 1Fh registers, power control registers address is coded on 5 bits. To get access to power control registers, both 1Eh and 1Fh registers must be used in a specific order.
1Fh register contains MSB (bits 3 and 4) of power control register address, and must be written first. 1Eh register contains LSB (bits 0 to 2) of Power control register address, data and EN (write) bit.
Table 2.
Power control registers with indirect addressing
I2C register 1Fh Reserved Power control address MSB LSB 0 7 6 5 4 3 2 1 0 I2C register 1Eh DATA EN
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6
5
4
3
2
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3.1
Indirect registers write
Indirect registers write is performed in two steps:
Write MSB of power control register address in I2C register 1Fh Write LSB of power control register address, data and EN=1 in I2C register 1Eh
3.1.1
Example
Power control register at address 05h, set Vcore to 1.34V (vcore_sel = 1100) Power control register address = 05h = 0000 0101 = 000 00 101 Address[4:3] = 00 -> write 0 0 00 00 = 0000 0000 = 00h at I2C address 1Fh Address[2:0] = 101 Data = 1100 EN = 1 -> write 101 1100 1 = 1011 1001 = B9h at address 1Eh
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Power control registers with indirect addressing
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3.1.2
C code example
void STw481x_power_control_write(unsigned char PCR_address, unsigned char data) { unsigned char temp_address = 0; unsigned char temp_data = 0; temp_address = (PCR_address >> 3) & 0x03; STw481x_main_I2C_write(0x1F, temp_address); temp_address = (PCR_address << 5) & 0xE0; temp_data = (data << 0x01) & 0x1E; temp_data |= 0x01; temp_data += temp_address; STw481x_main_I2C_write(0x1E, temp_data); }
3.2
Indirect registers read
As LSB of power control register and of register data are written simultaneously in the same I2C register, it is not easy to re-read data from the power control registers. Register 1Fh must be written with EN=0 (no data write, only LSB of address take into account), then the 1Eh register must be read. This provides in return the corresponding power register address LSB and data.
Write MSB of power control register address in I2C register 1Fh Write LSB of power control register address, dummy data (0000) and EN=0 in I2C register 1Eh Read register 1Eh to get the LSB of power control register and data.
3.2.1
Example
Power control register at address 09h, read Power control register address = 09h = 0000 1001 = 000 01 001 Address[4:3] = 01 -> write 0 0 00 01 = 0000 0001 = 01h at I2C address 1Fh Address[2:0] = 001 Data = 0000 EN = 0 -> write 001 0000 0 = 0010 0000 = 20h at address 1Eh -> Read at I2C address 1Eh Returned value = 3Eh = 0011 1110 = 001 1111 0 Address[2:0] = 001 Data = 1111 -> data[3]: vaux_sleep = 1 data[2]: reserved = 1 data[1]: vio_vmem_sleep = 1 data[0]: vcore_sleep = 1 EN = 0
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Power control registers with indirect addressing
3.2.2
C code example
unsigned char STw481x_power_control_read(unsigned char PCR_address) { unsigned char temp_address = 0; unsigned char temp_data = 0; temp_address = (PCR_address >> 3) & 0x03; STw481x_main_I2C_write(0x1F, temp_address); temp_address = (PCR_address << 5) & 0xE0; temp_data = temp_address; STw481x_main_I2C_write(0x1E, temp_data); temp_data = STw481x_main_I2C_read(0x1E); temp_data = (temp_data >> 1) & 0x0F; return temp_data; }
3.3
Changing an indirect register value
To change some bits of an indirect accessed register without changing undesired bits proceed as follows: read the indirect register change the desired bits read the result which was written in the corresponding indirect register
3.3.1
Example: merging USB I2C and main I2C
To merge both I2C buses, set bit usb_i2c_ctrl (bit 0 of power control register 06h) to access USB registers through the main I2C interface. Read data in 06h power control register, write `1' as bit 0 value, and then write the corresponding value into power control register 06h.
C code example
void STw481x_merge_I2C() { unsigned char data = 0; data = STw481x_power_control_read(0x06); data |= 0x01; STw481x_power_control_write(0x06, data); }
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USB I2C registers
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3.3.2
Example: splitting USB I2C and main I2C
To split the two I2C buses, reset bit usb_i2c_ctrl (bit 0 of power control register 06h), to access separately USB registers through the dedicated I2C_USB bus. Read data in 06h power control register, write `0' as bit 0 value, and then write the corresponding value into power control register 06h.
C code example
void STw481x_split_I2C() { char data = 0; data = STw481x_power_control_read(0x06); data &= 0x0E; STw481x_power_control_write(0x06, data); }
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USB I2C registers
USB registers (00h to 10h) can be accessed using two methods:
Using two different I2C buses, USBSDA and USBSCL connected to an I2C controller. Device ID is 5Ah (01011010) in read mode and 5Bh (01011011) in write mode. Using the main I2C interface, so that USB and power management registers are accessed using the same interface.
By default, the two I2C interfaces are separated. To enable access to USB registers from the main I2C, usb_i2c_ctrl (power control register 06h, bit 0) must be set to 1 using indirect addressing as described in Chapter 3: Power control registers with indirect addressing.
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Revision history
Table 3.
Date 05-Oct-2007
Document revision history
Revision 1 Initial release. Changes
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