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TTL and CMOS Compatibility of Digital I/O lines on the NI-78xxR Series Boards

Hardware: Reconfigurable I/O (RIO)>>R Series

Problem:
Are the digital lines on 78xx series RIO FPGA devices compatible with CMOS and/or TTL logic?

Solution:
The digital input and output lines of the 78xx series devices are compatible with almost all CMOS and TTL logic devices.

 

The following list describes compatibility of the digital I/O:

The 78xx can:
- Receive signals from 3V or 5V TTL or CMOS devices with no additional circuitry.
- Drive signals to 3V or 5V TTL devices with no additional circuitry.
- Drive signals to 3V CMOS devices with no additional circuitry.

The 78xx cannot:
- Directly drive a signal to a 5V CMOS device.  The Voh of the 78xx isn't high-enough to guarantee a valid logic high at the receiving device.  To fix this problem, all you have to do is add an external pull-up resistor to 5V on the digital output line.

Related Links:
KnowledgeBase 4QNHGPL1: Is it Possible to Configure a Digital Line on an R-series Board to a Tri-State Mode in FPGA?

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Report Date: 06/08/2006
Last Updated: 08/13/2009
Document ID: 3Y79G91J

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