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What Is the Definition of a TTL (Transistor-Transistor Logic) Compatible Signal?

Hardware: Multifunction DAQ (MIO)

What is the definition of a TTL (Transistor-Transistor Logic) compatible signal?

A TTL signal must meet an output voltage and current specification, an input voltage and current specification, and a rise/fall time specification. For any given hardware, the signal must also have a minimum pulse width.
Note: All specifications use the following notation:
  • Output Low = OL
  • Output High = OH
  • Input Low = IL
  • Input High = IH
  1. The output voltage and current specifications are as follows:
    • VOL = 0.4 V
    • VOH = 2.4 V
    • IOL = 16 mA
    • IOH = 400 µA
  2. The input voltage and current specification are as follows:
    • VIL = 0.8 V
    • VIH = 2.0 V
    • IIL = 1.6 mA
    • IIH = 40 µA
  3. The maximum rise/fall time is 50 ns between VIL and VIH. The minimum pulse width for:
    • NI-STC devices is 10 ns.
    • NI-TIO devices is 5 ns.

Note: The ratio between IOL and IIL as well as IOH and IIH is 10 due to the standard fanout of TTL logic.

Related Links:
KnowledgeBase 16A9OC6O: What are the Basic Differences Between CMOS and TTL Signals?
KnowledgeBase 32UG8H6I: How Can I Use my Non-TTL Signal to Generate a TTL digital Signal?


Report Date: 07/19/2002
Last Updated: 10/08/2010
Document ID: 2NICQ15A

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