Texas Instruments SN74HC42NS

Overview

SN74HC42NS from Texas Instruments is a BCD-to-decimal decoder IC in 16-pin SOP (NS) package, operating from 2 V to 6 V supply, delivering ±4-mA output drive at 5 V, with typical propagation delay of 14 ns and maximum ICC of 80 µA - used for address decoding and numeric display selection in legacy digital systems.

For engineers reviewing the SN74HC42NS datasheet, SN74HC42NS pinout, SN74HC42NS application, or SN74HC42NS equivalent, this page provides verified functional identity, validated pin mapping, confirmed BCD decoding behavior, real-world timing specs, and direct alternative options for industrial control and retro-computing designs.

Technical Context

This device implements full BCD decoding using eight inverters and ten 4-input NAND gates, with all ten outputs active-low. Inputs A–D accept binary-coded decimal (0000–1001), and all outputs go high for invalid codes (1010–1111), ensuring fail-safe logic states.

It operates in standard CMOS logic family with rail-to-rail input thresholds (VIH = 3.15 V min at VCC = 4.5 V; VIL = 1.35 V max), supports up to 10 LSTTL loads, and features low input current (≤1 µA max) and low power consumption - making it suitable for mixed-logic interfacing and battery-sensitive applications.

Key Specifications

Pinout & Package

SN74HC42NS is supplied in a 16-pin Small Outline Package (SOP-NS), 300-mil body width, with gull-wing leads and standard JEDEC MO-153 footprint. Pin 1 is located at the top-left corner with polarity marker (notch or dot).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar BCD-to-decimal decoding applications.

Compared with SN74HC42NS, SN74LS42N consumes >200× more static power and lacks 2–3.3 V support, while 74HCT42PW trades wide-voltage flexibility for robust TTL input compatibility - making SN74HC42NS optimal for low-power, multi-supply BCD decoding where full voltage range matters.

Availability

SN74HC42NS is available at Aetrix Electronics and suitable for industrial panel meters, retro computing address decoding, and legacy test equipment displays requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74HC42NS includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions with global manufacturing and distribution infrastructure.

SN74HC42NS belongs to TI's legacy 74HC logic family, designed for pin-compatible replacement of bipolar TTL decoders while delivering CMOS power efficiency and wider supply tolerance.

FAQ

What is the primary function of the SN74HC42NS?

The SN74HC42NS is a BCD-to-decimal decoder that converts a 4-bit binary-coded decimal input (A–D) into ten active-low decimal outputs (0–9). It asserts exactly one output for valid BCD codes (0000–1001), and forces all outputs high for invalid inputs (1010–1111). This behavior is implemented via internal inverters and NAND gates, and is documented in the function table of the SN74HC42NS datasheet.

Does SN74HC42NS support 3.3 V operation?

Yes, SN74HC42NS supports 3.3 V operation within its specified 2 V to 6 V supply range. At VCC = 3.3 V, VIH is guaranteed ≥2.31 V and VIL ≤1.09 V per the recommended operating conditions table. The SN74HC42NS maintains full functionality including propagation delay (typical 18 ns at 3.3 V) and output drive (±4 mA scaled), making it suitable for mixed-voltage 3.3 V/5 V systems.

What happens when an invalid BCD code is applied to SN74HC42NS inputs?

When any invalid BCD code (1010 through 1111) is applied to the SN74HC42NS inputs, all ten outputs (pins 1–9 and 11) go high. This fail-safe behavior is hardwired in the logic diagram and confirmed in the function table. It prevents unintended activation of downstream devices such as displays or relays during power-up, reset, or counter overflow - a key design feature of the SN74HC42NS.

Can SN74HC42NS drive LEDs directly?

Yes, SN74HC42NS can drive common-anode LEDs directly when configured with appropriate current-limiting resistors. Each output delivers ±4 mA at 5 V, sufficient for low-current indicator LEDs. For example, with a 5 V supply and red LED (VF ≈ 1.8 V), a 680 Ω resistor yields ~4.7 mA - within SN74HC42NS specifications. Always verify VOL ≤ 0.33 V at 4 mA per the SN74HC42NS electrical characteristics table.

Is SN74HC42NS pin-compatible with SN74LS42N?

Yes, SN74HC42NS is pin-compatible with SN74LS42N in the 16-pin PDIP (N) and SOIC (D) packages, sharing identical pin assignments for inputs (A–D), outputs (0–9), VCC, and GND. However, SN74HC42NS uses SOP-NS packaging - physical compatibility requires verifying land pattern match. Electrical differences (voltage range, drive strength, timing) must be validated in the target application before substitution.