Monday, July 21, 2008

FPGA frequency counter code.

An FPGA project that does something useful: implements a frequency counter using the Xilinx Spartan 3AN development board. Basically consists of two counters and the AX8 uC core. The first counter generates a 1 Hz timing signal from the on-board 50 MHz crystal oscillator, and the second counter counts the signal under test. The AX8 core runs a simple program that reads the count value and formats it for display on the LCD.
The attached image is counting the frequency of a VEX RC transmitter using a 75.97 MHz crystal. The measured count is 75.971459 MHz, which is within 0.002% of the expected value. The development board uses an xtal oscillator marked AGXO-751L 50.000 A. I found a datasheet at indicating that A versions are 100ppm, or 0.01%, so the measured value is well inside the tolerances.
I'll be posting the code when I get it ready.

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