Definition of a TTL (Transistor-Transistor Logic) Compatible Signal

Updated Apr 11, 2019

Reported In

Hardware

• Multifunction I/O Device
• C Series Multifunction I/O Module
• C Series Differential Digital I/O Module

• NI-DAQmx

Issue Details

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

Solution

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

The output voltage and current specifications are as follows:
• VOL = 0.4 V
• VOH = 2.4 V
• IOL = 16 mA
• IOH = 400 µA

The input voltage and current specification are as follows:
• VIL = 0.8 V
• VIH = 2.0 V
• IIL = 1.6 mA
• IIH = 40 µA

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.