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CMOS Image sensor & Two-wire serial interface

Discussion in 'Embedded' started by Kcin, Nov 26, 2008.

  1. Kcin

    Kcin Guest

    Hi, I tried to look for similar topics in the archive but no luck.

    I have a cmos image sensor, and it has a "two-wire serial interface"
    to read/write its on-chip registers. I tried to treat it like a I2C
    protocol, and fed a 100KHz at SCL, and write an address byte at SDA,
    but cannot get the acknowledge bit.

    Is it about the values of pull-up resistors in SCL and SDA? Or the
    clocking frequency problem??

    Thanks.

    Kcin
     
    Kcin, Nov 26, 2008
    #1
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  2. Kcin

    Kcin Guest

    It's a Micron's CMOS image sensor. The spec only describes both SCL
    and SDA should be pull up 3.3V with a 1.5k ohm resistors. No suggested
    clock rate of SCL. It does not have any signs of the word "i2c" as
    well, it calls it "Two-Wire Serial Interface". What standard is it
    really?

    "Serial Bus Description
    Registers are written to and read from the MT9T001 through the two-
    wire serial interface bus. The MT9T001 is a two-wire serial interface
    slave and is controlled by the two-wire serial clock (SCLK), which is
    driven by the two-wire serial interface master. Data is transferred
    into and out through the MT9T001 through the two-wire serial interface
    data (SDATA)
    line. The SDATA line is pulled up to 3.3V off-chip by a 1.5KÙ
    resistor. Either the slave or master device can pull the SDATA line
    down--the two-wire serial interface protocol determines which device is
    allowed to pull the SDATA line down at any given time."
     
    Kcin, Nov 27, 2008
    #2
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  3. I2C interfaces often aren't called I2C, presumably due to possible licensing/patent issues or subtle
    implementration differences. However the required waveforms will be in the datasheet.
     
    Mike Harrison, Nov 27, 2008
    #3
  4. Kcin

    jakiechon Guest

    I am actually working on the same thing and can not get an acknowledge
    either.

    I am running from the LH a SCL of 100KHz and my PIXCLOCK (which is the
    master for the MT9T001) at ~ 2.5 MHz.

    For some reason I still cannot get an acknowledge bit on I2C.

    I checked the timing diagrams and a 2.5MHz clock should meet the
    minimum by far, but still nothing...

    Anybody got any ideas?

    --Daniel
     
    jakiechon, Nov 29, 2008
    #4
  5. Kcin

    Kcin Guest

    I tried to feed 100KHz and 400KHz to SCL @ 48MHz master clock, but
    still no ack bit.

    I will try to lower SCL to 80KHz.

    More, I am wondering if SCL depends on the master clock.

    I read several specs and it seems that many of their cmos run with
    this "2-wire serial interface". What is the trick really?

    Thanks.

    Kicn
     
    Kcin, Nov 29, 2008
    #5
  6. Which timings have you checked? Video or I2C?

    I would actually suggesting capturing your I2C communications on
    a digital scope and checking what is happening and that your are sending
    the right information.

    Often these sorts of problems end up as

    Incorrect bit pattern (address/data)
    Incorrect waiting for bit times
    incorrect or open connections
    incorrect voltage levels used
    incorrect I2C termination
    incorrect oscillator on imager
    Some other configuration on the imager missing/wrong

    It is very, very rarely the device at fault, sometimes the documentation.
    --
    Paul Carpenter |
    <http://www.pcserviceselectronics.co.uk/> PC Services
    <http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font
    <http://www.gnuh8.org.uk/> GNU H8 - compiler & Renesas H8/H8S/H8 Tiny
    <http://www.badweb.org.uk/> For those web sites you hate
     
    Paul Carpenter, Jun 30, 2010
    #6
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