TTL/CMOS Compatibility With Counter and Digital Modules

Updated Dec 13, 2023

Reported In

Hardware

  • Counter/Timer Device
  • Digital I/O Device

Issue Details

  • I have a Counter/Timer module or a Digital I/O and I want to know if it is compatible with TTL/CMOS logic levels. 
  • I want to use my NI module with a CMOS input/output, but the Logic Level Table in the datasheet indicates voltage values that are not withing the ranges for TTL and CMOS. Is the device still compatible?

Solution

To find out if a device is compatible with TTL/CMOS logic levels, you should refer to the specifications of your device and find the compatibility in the I/O Characteristics section:

TTL CMOS comp.png

This means that NI has tested these cards with typical TTL/CMOS inputs or outputs and confirmed that the logic levels are read/written correctly from the cards, considering the voltage, impedance, and current handled by TTL/CMOS inputs/outputs. 

Additional Information

Notice there is also a Digital Logic Levels table in the specifications of the device:

digital logic levels.png

This table can be used when the device that will interface the NI module is not a TTL/CMOS device, so the information on this table should be taken into account for that custom design. 

If the device that will interface the NI module is TTL/CMOS, this table can be ignored. 

Related Links

Choosing the Right Industrial Digital I/O Module for Your Digital Output Sensor

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