Subelement E: Digital Logic— Topic 33: Types of Logic
Question 3-33E1
Element 3 (GROL)What is the voltage range considered to be valid logic low input in a TTL device operating at 5 volts?
Explanation
TTL (Transistor-Transistor Logic) devices operate with specific voltage thresholds to differentiate between a logic '0' (low) and a logic '1' (high). For a standard 5-volt TTL integrated circuit, a valid logic low input (VIL, Voltage Input Low) is defined as any voltage from zero volts up to a maximum of 0.8 volts. This ensures the input transistor within the TTL gate is properly driven into saturation, correctly interpreting the signal as a logic '0'.
Options A, B, and D are incorrect. Option A describes a range that overlaps with the logic high input (VIH), which is typically 2.0V to 5V. Options B and D present negative voltages or voltages far exceeding the nominal 5V operating voltage of TTL, which are incorrect and could damage the device.
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