Using the slow DAC from FPGA

[fisp]

Hello,

I'm currently working in a project where I'm writing my own FPGA program for the Red Pitaya STEMlab 125-14 .
So far using the fast ADC and DAC is working out fine, but I also need to use 2 channels of the slow DAC outputs. I can't find any information in the documentation how to control the output voltage. The FPGA constrains contain 4 "dac_pwm_o" pins, but I can't find out how to design the PWM signal.

By playing around with different PWM signals I was able to generate a saw-tooth-like voltage, but I would like to be able to adjust a stable output voltage between the 0 to 1.8 V. Is there any information available on how to achieve that?

Thanks,
Finn

[juretrn]

Hi,
the current FPGA implementation uses a PDM-based slow DAC (red_pitaya_pdm). The configuration for this module is 4x 8 bit values, where 0 represents 0 V and 255 is 1.8 V. The output of that PDM is then passed through an RC filter, which should give an appropriate DC signal.

[fisp]

Hi,

thanks for your fast reply and your hints! I got the slw DAC working.

[ZQInreal]

Hi,
the current FPGA implementation uses a PDM-based slow DAC (red_pitaya_pdm). The configuration for this module is 4x 8 bit values, where 0 represents 0 V and 255 is 1.8 V. The output of that PDM is then passed through an RC filter, which should give an appropriate DC signal.

Hello, I see that the slow DAC has a 12-bit resolution. Why is the PDM module only 8 bits ?

[juretrn]

What "slow DAC" are you thinking of?
The one in question is a single line that gets passed through an analog filter, which gives the appropriate DC voltage.

Are you looking at the Zynq's on-board XADC module? That is an ADC only.