Re: Problems with I2C reads

[bhupinder sahran <bhup_sah@yahoo.com>]

hi

I think u r missing onr thing.

sequence should be like this


> Start signal
> Slave address (r/w/ bit = write)
> Register address
> Start signal
> Slave address (r/w/ bit = read)
> Read register data
>NO ack.......................u have to give
> Stop signal


Try to give No ack after reading the register data.

bye
Bhupi
Deep  into silicon with Linux.....
www.gdatech.com

--- Keith Outwater <Keith_Outwater@mvis.com> wrote:
>
> Greetings all -
>
> I am trying to talk to an I2C device (Analog Devices
> AD9888) using the
> MPC860 CPM I2C interface from userland.
> Writes work fine, but the chip requires a strange
> write-read sequence
> for reading back registers.  For example, to read a
> register:
>
> Start signal
> Slave address (r/w/ bit = write)
> Register address
> Start signal
> Slave address (r/w/ bit = read)
> Read register data
> Stop signal
>
> Note that there is no stop between the write and the
> read.  If you put a
> stop in, the chip will not acknowledge the read, so
> using /dev/i2c-0
> with write() and read() does not work.
>
> I tried using the ioctl() interface and passed
> I2C_RDWR to try to
> suppress the stop command between messages, but it
> does not seem to work
> (checked it on a scope).
> I looked at the ioctl() handler for I2C_RDWR and it
> was not clear to me
> whether that particular ioctl option should work
> with a write-read
> sequence or not.  As far as I can tell it does not
> work.
> I looked for other ways to do this, but found
> nothing.
>
> Has anyone used I2C like this before? Any hints or
> suggestions?
>
> Thanks!
> Keith
>
> Keith Outwater
> Senior Staff Engineer
> Microvision, Inc.
> (425) 415-6693
>
>
>


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