i2c question (BBB)

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1

I’m trying i2c bus on BBB

slave module is OV7670 ( CMOS Camera )

OS is angstrom

when i connect ov7670 on BBB P9 Header (19,20)

and command i2cdetect -r -y 1

look at the picture above you fine ‘21’ is creating

0x21 is slave address ???

but slave address of ov7670 is 0x42 in datasheet

what means 0x21 ??

and

am i better try i2c ???

My purpose is writing data to the ov7670 register.

Advice please

2

There is an “8 bit” representation of an I2C address, where the bottom bit is actually the Read/Write bit and is, by convention, set to zero to describe the address.
There is a “7-bit” representation of an I2C address, where the address is shifted one bit to the right, so the read/write bit disappears and is not part of the address.
Half the manufacturers do it one way, the other half the other way.

Linux/Debian uses the 7 bit representation.

0x42 >> 1 = 0x21

— Graham

3

thank you for your answer

When the ‘1’ shift is not this lead?

Then how to i write register in Ov7670 ??

I must register modification in OV7670

I wonder how to I2C write .

*Please understand the lack of my English skills. ^^ ;;;;

thanks

2015년 6월 25일 목요일 오전 2시 18분 37초 UTC+9, Graham 님의 말:

4

The signal on the bus is the same.
Just the name is different.

So to talk to the part using Linux, use the address in “7-bit” format, which for your part is 0x21.

If you are writing in C, you will use i2c-dev and ioctl

If you are writing in Python 2.7, you will use SMbus and something like the Adafruit Python I2C BBB-IO

Best regards,

— Graham