Help with VGA on Digilent Nexys2 : Monitor displays blank

[karvin89]

Hi,

Problem: Monitor displays blank state

I am trying to display images on a monitor. I am using the VGA controller code provided by Digilent that uses a 25Mhz from a DCM and outputs HS and VS signals (which I tested for correct timing). The controller also provides two 11bit horizontal (vecHcount_640_60) and vertical (vecVcount_640_60) pixel address counter buses. I have instantiated this controller in a main VHDL module that communicates with the Microblaze and also provides a 6336 (88 x 72) 8bit byte array which I intend to use as Video ram. The board has termination resistors for 8-bit RGB data. Digilent's built in test code works and displays some psychedelic stuff.

    type ram_type is array (0 to 2** 13) of std_logic_vector( 0 to 7) ;
    signal video_ram : ram_type; 

-----  I use  the following code bit to map the 11 bit buses to the video ram.

    RGB_OUT_temp <= video_ram(conv_integer(conv_integer(vecHcount_640_60)+(88*conv_integer(vecVcount_640_60))))   
                            when ((vecHcount_640_60 < 88) AND (vecVcount_640_60 < 72)) else (others => '0');
   
    --RGB_OUT <= RGB_OUT_temp when bitBlank640_60 = '1' else (others => '0');
    RGB_OUT <= "10100100";

As you can see, I even tried setting RGB_OUT to some random color and the monitor is still blank. Monitor seems to recognize HS and VS which I already verified on an oscilloscope.

Is there something fundamental I am missing here? I looked into a couple of other example codes but did not notice anything odd.


Regards,

Karthik