Texas Instruments SN74LS148NSR

Overview

SN74LS148NSR from Texas Instruments is a TTL 8-line-to-3-line priority encoder IC that converts active-low octal inputs (I₀–I₇) into active-low 3-bit binary outputs (A₀–A₂), with enable input (EI), group signal (GS), and enable output (EO) for cascading. It operates at 5 V, delivers 15 ns typical propagation delay, draws 12–20 mA supply current, and supports industrial temperature range (0°C to 70°C). It is used in keyboard encoding, interrupt prioritization, and digital system address encoding.

For engineers reviewing the SN74LS148NSR datasheet, SN74LS148NSR pinout, SN74LS148NSR application, or SN74LS148NSR equivalent, this page provides verified functional identity, validated SOP-16 pin mapping, confirmed low-level active logic behavior, cascading interface timing, and real-world design constraints including transient GS glitches during EI transitions and input loading requirements (9 kΩ for I₁–I₇).

Technical Context

The SN74LS148NSR implements combinational priority encoding logic where only the highest-order asserted (low) input determines the output code; lower-priority inputs are masked. Its internal architecture uses buffered TTL gates with normalized Series 74LS load compatibility (18 kΩ pull-up for non-I₁–I₇ inputs, 9 kΩ for I₁–I₇).

Cascading is enabled via EI (active-low enable input) and EO (active-low enable output), while GS (group signal, active-low) indicates whether any input is asserted. All inputs and outputs operate with active-low logic levels, requiring external pull-ups for proper interfacing in open-collector or wired-OR configurations.

Key Specifications

Pinout & Package

SOP-16 (NS package), 2.00 mm max height, 16-pin surface-mount small-outline package with 1.27 mm pitch; pin 1 marked by beveled corner or notch; RoHS-compliant NiPdAu lead finish; MSL Level-1 (unlimited floor life at ≤30°C/60% RH).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar priority encoder applications.

Compared with SN74LS148N and SN74LS148DR, the SN74LS148NSR offers optimized thermal performance (64°C/W θJA) and SOP-16 footprint compatibility with modern SMT lines, while maintaining identical encoding behavior, timing, and drive capability-making it ideal for volume production of compact industrial controllers.

Availability

SN74LS148NSR is available at Aetrix Electronics and suitable for keyboard encoding, interrupt prioritization, industrial control panels, and digital system address encoding requiring stable component supply across commercial temperature ranges.

Supply support for SN74LS148NSR 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 and embedded processing technologies with broad industrial, automotive, and consumer product portfolios.

The SN74LS148NSR belongs to TI's legacy 74LS logic family, designed for low-power, medium-speed TTL-compatible digital systems where deterministic priority resolution and cascading capability are essential-particularly in retrofitted industrial controls and education platforms.

FAQ

What is the primary function of the SN74LS148NSR?

The SN74LS148NSR is an 8-line-to-3-line priority encoder that converts eight active-low inputs (I₀–I₇) into a three-bit active-low binary output (A₀–A₂), with built-in priority resolution so only the highest-order asserted input determines the code. It also provides group signal (GS) and enable output (EO) for cascading. This function is fixed in silicon and cannot be reconfigured.

How does the SN74LS148NSR handle multiple simultaneous low inputs?

The SN74LS148NSR resolves multiple simultaneous low inputs using hardwired priority logic: I₇ has highest priority and masks I₆ through I₀, I₆ masks I₅ through I₀, and so on down to I₀ as lowest priority. The output reflects only the highest-priority asserted input; no arbitration delay or external logic is needed. This behavior is inherent to the SN74LS148NSR's gate-level design.

What are the critical timing considerations when using the SN74LS148NSR in a synchronous design?

When integrating the SN74LS148NSR into synchronous logic, designers must account for its 14–25 ns propagation delays (tPHL/tPLH), input setup/hold timing relative to EI transitions, and transient GS glitches that occur on EI falling edges-even when all inputs are high. These characteristics are documented in the SN74LS148NSR datasheet Figures 1 and 2 and require strobing the outputs after sufficient delay or using GS as a valid-data qualifier.

Can the SN74LS148NSR be used without external pull-up resistors?

No-the SN74LS148NSR has totem-pole outputs but requires external pull-up resistors on all inputs (I₀–I₇, EI) and outputs (A₀–A₂, GS, EO) to establish valid TTL logic levels, because its inputs are current-sinking and outputs are designed for driving TTL loads-not open-drain operation. Typical pull-up values are 10 kΩ for outputs and matched to input impedance (9 kΩ for I₁–I₇, 18 kΩ for I₀/EI) per the SN74LS148NSR datasheet Section 6.

Is the SN74LS148NSR suitable for new designs given its legacy status?

Yes-the SN74LS148NSR remains actively produced (TI status: "Active") in SOP-16 tape-and-reel packaging (2000 units/reel), with full datasheet support, guaranteed supply chain continuity, and qualification for 0°C to 70°C operation. While newer CMOS alternatives exist, the SN74LS148NSR is preferred where TTL-level compatibility, known timing margins, and drop-in replacement for legacy 74LS systems are required-especially in industrial maintenance and backward-compatible upgrades.