Interfacing one logic family with another

Discussion in 'Digital Circuit Design' started by electrophile, Aug 6, 2016.

  1. electrophile

    Thread Starter Member

    Aug 30, 2013
    Would the interfacing in the attached image work? The buffer and OR gate are LVC family chips. The MCU input is from an Atmega328 AVR. VHC is apparently a speed upgrade for the HC family. Everything is powered with a 5V supply.

    Last edited: Aug 6, 2016
  2. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
    Did you check the datasheets for these devices and compare their input/output voltage specifications?
  3. Papabravo


    Feb 24, 2006
    If all chips run from a VCC of +5V including the AVR then it will be fine. You should have a pullup resistor on the input to the LVC buffer to prevent it from oscillating when the switch is open.
  4. electrophile

    Thread Starter Member

    Aug 30, 2013
    Yep! they do seem to all operate within the specs. Did some more research on this and the LVC is designed to run with 3.3V supplies (though quite a few now specify that they can also be powered with 5V) and hence its Voh is at 2.4V and the Vih of the VHC is at 3.5V. Hence in a mixed environment this may not work. However since everything is powered with 5V and the LVC are 5V tolerant, there shouldn't be a problem in this specific case.
    Thanks. That helps!
  5. hp1729

    Well-Known Member

    Nov 23, 2015
    Yes, pullup resistor on the LVC input. Check your data sheets. The LVC can drive 24 mA to either rail. The VHC is not needed and may be an open drain output.