Implementation Issue

Hi Guys,

I'm using the Spartan-3E 1600E Microblaze development kit.
What I'm basically doing is writing to the on board DAC (Linear Tech
LTC2624 Quad DAC), and then reading from the on board ADC (Linear Tech
LTC6912 Dual A/D) whose analog input is connected to the DAC analog output.
The data written to the DAC and the data read from the ADC is then made
available to other modules within my design for analysis/comparison and is
also made available to my LCD driver module so as to display the data on
the LCD.

The problem that I am having is that no data is read back from the ADC (ADC
data displayed on LCD is all 0s), however the DAC was successfully written
to (DAC output voltage changed correctly). Now initially I thought I must
be reading from the ADC incorrectly so I simply brought out debug signals
to a header on the board (J4) so that they could be viewed with an
oscilloscope. The debug signals were connected to the SPI interface signals
TCK, MOSI, MISO, and ADCconv. After bringing out these debug signals, which
should not effect the design, the design then worked and ADC data was being
read back correctly.

Now when any combination of the ucf contraints that assign the debug
signals to the header pins are commented out and the design is
re-implemented (not res-synthesised) the design does not work.
 
Does anyone have any ideas about this? Any help would be greatly
appreciated.
 
Regards,
James

	   
					
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In article <_9GdnRsyfMSQXR3TnZ2dnUVZ_rydnZ2d@giganews.com>,
James <james.gahan@n_o_s_p_a_m.analog.com> wrote:
>Hi Guys,
>
>I'm using the Spartan-3E 1600E Microblaze development kit.
>What I'm basically doing is writing to the on board DAC (Linear Tech
>LTC2624 Quad DAC), and then reading from the on board ADC (Linear Tech
>LTC6912 Dual A/D) whose analog input is connected to the DAC analog output.
>The data written to the DAC and the data read from the ADC is then made
>available to other modules within my design for analysis/comparison and is
>also made available to my LCD driver module so as to display the data on
>the LCD.
>
>The problem that I am having is that no data is read back from the ADC (ADC
>data displayed on LCD is all 0s), however the DAC was successfully written
>to (DAC output voltage changed correctly). Now initially I thought I must
>be reading from the ADC incorrectly so I simply brought out debug signals
>to a header on the board (J4) so that they could be viewed with an
>oscilloscope. The debug signals were connected to the SPI interface signals
>TCK, MOSI, MISO, and ADCconv. After bringing out these debug signals, which
>should not effect the design, the design then worked and ADC data was being
>read back correctly.
>
>Now when any combination of the ucf contraints that assign the debug
>signals to the header pins are commented out and the design is
>re-implemented (not res-synthesised) the design does not work.

Timing constraints on the SPI input?  Do they exist?  Do they pass timing
analysis - for both implementations (with and without the debug connections)?

Depending on how/where you brought out the debug connections, it may 
affect timing greatly.  If you're not having the tool check the timing,
you're just rolling the dice.

Regards,

Mark

>In article <_9GdnRsyfMSQXR3TnZ2dnUVZ_rydnZ2d@giganews.com>,

Thanks for the help.

As you could probably guess I'm new to setting timing constraints and
analysing timing results.
Is there any literature or documentation that you could recommend that
might help me?

Regards,
James
	   
					
---------------------------------------		
Posted through http://www.FPGARelated.com

>>In article <_9GdnRsyfMSQXR3TnZ2dnUVZ_rydnZ2d@giganews.com>,
>
>Thanks for the help.
>
>As you could probably guess I'm new to setting timing constraints and
>analysing timing results.
>Is there any literature or documentation that you could recommend that
>might help me?
>
>Regards,
>James
>

http://forums.xilinx.com/t5/PLD-Blog/Timing-Constraints-Part-1-of-5/ba-p/57594
	   
					
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