Re: OV7620 image sensor interface with FPGA headache

From: dalle002 (dwmunandar_at_yahoo.com)
Date: 11/19/04 

Date: Fri, 19 Nov 2004 00:15:12 -0500

Dear helpers,

Your inputs were awesome. I made sure the I2C was enabled, put a 4k7
pullup resistor and make sure the timing specifications are met and BAM!
it works! I got the acknowledge signals and the PCLK frequency has doubled
to 27MHZ. I was jumping up and down for a while in gladness. Thank you all
for your help. Probably my biggest mistake is the 300k resistor I used.

Now I still need further help on sending the image to the VGA monitor. Did
anyone has succesfully send the digital image directly to a monitor
without any need of storing the image in a memory?

I tried to store the pixel information in registers that is output to the
color signals to the monitor. I noticed with progressive 16-bit mode, the
UV channel output G and R values in sequence, and the Y channel output B
and G values. I noticed that the register go some values but if I use the
VSYNC and HREF signal from the camera sent directly to the monitor,
nothing showed up.

I also use the FPGA to count numbers of HSYNC in a frame. The FPGA counted
about 424 HREF signals plus minus 10 more. I'm wondering how come the
number is not consistent? And why is it not close to 492 (I'm expecting
492 lines for VGA output).

I'm wondering if this is because the sampling clock my FPGA use (50MHz) is
not sufficient to sample the pixel information (13MHz) for progressive,
RGB, 16-bit mode? Would anyone recommend taking out the camera's
oscillator, connect the JP1 jumper and give the camera and external clock
from the FPGA?

I also noticed a discrepancy in the camera's data sheets. It says that if
it were to be set as a slave with an external clock provided, the VSYNC
signal must be provided to the camera. The VSYNC signal must follow the
formula: 525*2*858*Tclk - which will only give about 30Hz/fps for an 25MHz
clock input? I need a 60Hz output for the monitor. Currently with the
camera's original oscillator, I observed 60Hz VSYNC signal given by the
camera. Why the disagreement?

Can anyone offer me any help on these questions? Any amount of input will
be appreciated.

Thanks ahead.