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How Do I Interface TTL Signals With CMOS Circuits?



Hardware: Multifunction DAQ (MIO)

Problem:
I want to interface my digital lines on my National Instruments DAQ board to my CMOS circuit. How can I interface the two? How do I connect two digital signals with different voltage levels?

Solution:
The following figures demonstrate how to interface a TTL signal to a CMOS circuit and a CMOS circuit to a TTL input. The figures also show how to interface the two circuits if the voltage levels are incompatible.


Figure 1: TTL-to-CMOS interfacing using pull-up resistor


Figure 2: CMOS-to-TTL interfacing using a CMOS buffer IC


Figure 3: TTL-to-CMOS interfacing using a transistor


Figure 4: TTL-to-CMOS interfacing using a TLL open-collector buffer IC


Figure 5: CMOS-to-TTL interfacing using a CMOS buffer IC

(Roger L. Tokheim, Digital Electronics, 3d ed., McGraw-Hill, New York, 1990)

Related Links:
KnowledgeBase 2NICQ15A: What Is the Definition of a TTL (Transistor-Transistor Logic) Compatible Signal?
Knowledgebase 1QJC94NV: 3.3 Volt TTL from Digital Products
Knowledgebase 16A9OC6O: What are the Basic Differences Between CMOS and TTL Signals?

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Report Date: 11/02/2003
Last Updated: 11/28/2012
Document ID: 331LET6I

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