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In a mixed environment, where the circuitry is not pure digital, follow the steps below.
1.
Connect TINALab II with your XC2S FPGA card as described under TINALab II User
Port on page 7.
2.
Open the \EXAMPLES\VHDL\FPGA\FPGA_Wave_Generator.TSC sample design.
The main digital logic (Digital wave) generates sine or saw binary sample values which are
fed into an R/2R resistor ladder network to form analog output signal on node DAC
output. The resistors functions as simple DAC, they are mounted on the FPGA board. The
Rp and Cp components are to model the TINALab II Oscilloscope Probe. If we perform
measurement by the instrument on the card, the Probe will affect the output signal. The
PreScaler divides 50M to 1MHz.
3.
Now, set the ‘Digital wave’ enable input to H and sel to L. Switch Probe off. Run transient
simulation: Anlysis > Transient… Enter 100u to the End Display value. Run transient
calculation with Probe on. As a result of calculating with the oscilloscope probe, which
imposes a loading of a parallel RC network, the step-like shape of the curve rolls more
slowly. The probe filters the high frequencies.
Note, the digital outputs are powered by VCCIO which value (3.3V) is identical that of the
FPGA chip is supplied on the board.
Содержание TINALab II
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