I am planning to use USB 6221 instead of USB 6501 DAQ in my application. In case of 6501 (open drain) and added a resistor from pin to gnd (4.7K pull up already present in 6501) to convert 5v digital signals to 3.3V digital signals. I couldnt find the output structure of 6221. Is it open drain or active push-pull. (first option - same as 6501, second option : i need a res divider sturcture from the digital pin)
Is there any major difference (compatability-wise) between 6501 and 6221
The USB-6221 only has a range of 0-5V and this is not programmable, so you will need external components to bring it to your needs.
Compatibility-wise, the two devices will not show differences in your project. As soon as you change the physical channels in your DAQmx tasks, you will be able to run your project with no problems.
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The 6221 is active push-pull when used as an output.
When choosing resistor values to divide-down your voltage, keep in mind that the DIO lines have an internal ~50k Ohm pull-down resistor (20k Ohm minimum).