Texas Instruments SN74LS42NSRE4

Overview

SN74LS42NSRE4 from Texas Instruments is a TTL BCD-to-decimal decoder IC that converts 4-bit binary-coded decimal input into active-low 10-line decimal outputs, with typical propagation delay of 45 ns at VCC = 5 V and output drive capability of 8 mA sink per line, used in address decoding and numeric display driver circuits.

For engineers reviewing the SN74LS42NSRE4 datasheet, SN74LS42NSRE4 pinout, SN74LS42NSRE4 application, or SN74LS42NSRE4 equivalent, this page delivers verified package mapping (PDIP-16), confirmed logic function (active-low decoded outputs), supply voltage range (4.75–5.25 V), and direct alternatives for legacy TTL system upgrades.

Technical Context

This device implements combinational logic decoding using standard TTL bipolar transistor-transistor logic architecture, with open-collector outputs requiring external pull-up resistors. It operates exclusively on a single +5-V supply and does not support enable inputs or cascading without external gating.

All ten outputs are active-low and mutually exclusive - only one output is low for any valid BCD input (0000–1001); invalid inputs (1010–1111) drive all outputs high. Input thresholds and noise margins conform to standard LS-TTL specifications.

Key Specifications

Pinout & Package

SN74LS42NSRE4 is supplied in a 16-pin plastic dual in-line package (PDIP), with 0.3-inch body width and through-hole mounting. Pin spacing is 0.1 inch, and the package includes a notch for orientation identification.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS42NSRE4, SN74LS145N offers identical form and function with minor leakage trade-offs, while 74HC42N enables modern low-voltage operation but introduces interface compatibility constraints requiring redesign.

Availability

SN74LS42NSRE4 is available at Aetrix Electronics and suitable for legacy system repair, industrial panel instrumentation, and educational electronics labs requiring stable component supply of through-hole TTL logic.

Supply support for SN74LS42NSRE4 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 ICs with broad industrial and automotive qualification.

The SN74LS42NSRE4 belongs to TI's legacy 74LS logic family, designed specifically for reliable, low-cost digital control and interface functions in commercial-grade equipment from the 1970s–1990s.

FAQ

What is the operating voltage range for SN74LS42NSRE4?

The SN74LS42NSRE4 operates strictly within 4.75 V to 5.25 V. It is not tolerant of under-voltage or over-voltage conditions outside this window, and operation below 4.75 V may cause incorrect output states or increased propagation delay. The SN74LS42NSRE4 requires a well-regulated +5-V supply with local 0.1-µF ceramic decoupling at the VCC pin.

Does SN74LS42NSRE4 have an enable input?

No, the SN74LS42NSRE4 does not include an enable input or any control pin beyond the four BCD inputs and ten outputs. It is a permanently enabled decoder - all outputs respond immediately to input changes. If system-level enable functionality is required, external gating (e.g., NAND gate) must be added to the inputs or outputs of the SN74LS42NSRE4.

What package type is used for SN74LS42NSRE4?

SN74LS42NSRE4 uses a 16-pin plastic dual in-line package (PDIP) with 0.3-inch body width and through-hole leads. The "N" suffix in the part number explicitly denotes PDIP packaging, and the "SRE4" suffix indicates tape-and-reel packaging per TI's internal ordering convention for legacy devices.

Can SN74LS42NSRE4 drive LEDs directly?

Yes, SN74LS42NSRE4 can drive common-anode LEDs directly using its open-collector outputs. With a 330-Ω pull-up resistor to +5 V, each output delivers ~8 mA sink current - sufficient for standard indicator LEDs. Ensure total package power dissipation remains within 500 mW, especially when multiple outputs are active simultaneously.

How does SN74LS42NSRE4 handle invalid BCD inputs (10–15)?

For invalid BCD inputs (1010 through 1111), the SN74LS42NSRE4 drives all ten outputs high (open-circuit state). This behavior is defined in the original SDLS109 datasheet and ensures predictable, non-ambiguous output states - critical for fault-tolerant decoding in safety-critical or diagnostic subsystems using the SN74LS42NSRE4.