Omnivision OV7640 SCCB (I2C?) bus problem

Paul Olley wrote:
> 
> >>    Part 1.1    Type: Plain Text (text/plain)
> >>            Encoding: quoted-printable
> >
> > Another unread message because of the html or mime encoding.
> > Usenet is a pure text mechanism.
> 
> Sorry!  I think it was as a result of cutting and pasting from the datasheet
> into the reply.

Misteaks happen :-)  At least you are aware of the problem.

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Thanks for your answers all ! and thanks for the schematic

Just another question, how long does it take for the camera to answe
the read address ? I'm waiting 50us, I thought it was enough, bu
apparently that could be the problem

> Just another question, how long does it take for the camera to answer
> the read address ? I'm waiting 50us, I thought it was enough, but
> apparently that could be the problem.

Do you mean, "How long does it take the camera to take the SCCB data line 
low during the acknowledge bit time? (ie : after the transmission of the 
address bits A7 to A1 and R/W?"

Or do I misunderstand your question?

When I looked at the ACK timing with my oscilloscope, I could clearly see 
the microcontroller releasing the data line, and the OV7640 taking the data 
line low to ack.  The low voltage levels were ever so slightly different, so 
it was easy to see the timing.  I will have to get the scope out again to 
make the measurement you may be asking for.

Paul.

On Wednesday, in article
     <aemdnSZKApHjNDvfRVn_vg@giganews.com>
     vincesusu@yahoo-dot-fr.no-spam.invalid "vinch" wrote:
>Thanks for your answers all ! and thanks for the schematic.
>
>Just another question, how long does it take for the camera to answer
>the read address ? I'm waiting 50us, I thought it was enough, but
>apparently that could be the problem.

50us from what?

From SCL set low for the ACK bit?
From SDA driven passive high?

What is the clock period for your address/data bits?

The fastest SCCB can be clocked is 100kHz, so 10us for each bit of
7 address bits, read/write bit, and ack bit, so the first address byte
is 9 x 10us = 90us MINIMUM plus start I2C timing.

If you are running at 100kHz, then wait at leat 90 if not 100us for the
whole address and ack, *IF* you are using some form of I2C controller.
If bit banging do a wait one each bit, slightly longer on ack.

You are still driving the SCL (SCCB clock) at that stage?

What frequency are you trying to drive SCCB at?

--
Paul Carpenter          | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/>    PC Services
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Yes, that's it
I can also see the microcontroller releasing the data line, but the
the level stays the same...

Thanks for the measurements 

> Paul Olleywrote
[quote:deef3a4c8b]Just another question, how long does it take fo
the camera to answe
> the read address ? I'm waiting 50us, I thought it was enough, bu
> apparently that could be the problem
>
Do you mean, "How long does it take the camera to take the SCCB dat
line
low during the acknowledge bit time? (ie : after the transmission o
the
address bits A7 to A1 and R/W?

Or do I misunderstand your question

When I looked at the ACK timing with my oscilloscope, I could clearl
see
the microcontroller releasing the data line, and the OV7640 taking th
data
line low to ack.  The low voltage levels were ever so slightl
different, so
it was easy to see the timing.  I will have to get the scope out agai
to
make the measurement you may be asking for

Paul.[/quote:deef3a4c8b

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>Part of my schematic, at least the part including the OV7640 is here : =
http://homepage.ntlworld.com/paul.olley/

Since the above webpage is still getting a significant number of hits 8 =
months later, to make the URL "permanent", I've copied the HTML to the =
following URL :
http://www.olley.com/ov7640/index.html

The original will disappear in due course.

Paul.
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Diso-8859-1">
<META content=3D"MSHTML 6.00.2900.2802" name=3DGENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV><FONT face=3DArial size=3D2>&gt;Part of my schematic, at least the =
part=20
including the OV7640 is here : <A=20
href=3D"http://homepage.ntlworld.com/paul.olley/">http://homepage.ntlworl=
d.com/paul.olley/</A></DIV>
<DIV>&nbsp;</DIV>
<DIV dir=3Dltr>
<DIV>Since the above&nbsp;webpage is still getting a significant number =
of hits=20
8 months later, to make the URL "permanent", I've copied the HTML to the =

following URL :</DIV>
<DIV><A=20
href=3D"http://www.olley.com/ov7640/index.html">http://www.olley.com/ov76=
40/index.html</A></DIV>
<DIV>&nbsp;</DIV>
<DIV>The original will disappear in due course.</DIV>
<DIV>&nbsp;</DIV>
<DIV>Paul.</DIV></DIV></FONT></BODY></HTML>

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