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.
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