Texas Instruments SN74LS148D

Overview

SN74LS148D from Texas Instruments is a TTL 8-line-to-3-line priority encoder IC with active-low inputs and outputs, 15 ns typical propagation delay, 60 mW typical power dissipation, and SOIC-16 package. It encodes eight data lines (0–7) into three-bit binary (A0–A2), supports cascading via EI/EO/GS pins, and is used in keyboard encoding and digital system address generation.

For engineers reviewing the SN74LS148D datasheet, SN74LS148D pinout, SN74LS148D application, or SN74LS148D equivalent, key selection considerations include active-low priority encoding logic, cascading capability for multi-bit systems, TTL-compatible input thresholds (VIL = 0.8 V, VIH = 2 V), and SOIC-16 thermal performance (θJA = 73°C/W).

Technical Context

The SN74LS148D implements combinational priority encoding where only the highest-order active-low input (lowest numeric index) determines the output code. Its internal logic ensures deterministic resolution of simultaneous low inputs without race conditions.

It features three active-low outputs (A0, A1, A2), two status flags - GS (Group Select, low when any input is active) and EO (Enable Output, low when all inputs are high and EI is low) - and one active-low enable input (EI). All inputs and outputs operate at standard TTL voltage levels with 4 mA sink / 400 µA source drive capability.

Key Specifications

Pinout & Package

SN74LS148D uses a 16-pin SOIC (Small Outline Integrated Circuit) package with 1.27 mm pitch, 10.0–10.4 mm body width, and 2.00 mm max height per TI NS0016A drawing.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS148N and SN74LS148DR, the SN74LS148D offers identical core encoding behavior but targets mid-volume SOIC assembly with tube packaging - balancing procurement flexibility and surface-mount compatibility without RoHS constraints.

Availability

SN74LS148D is available at Aetrix Electronics and suitable for keyboard encoding, industrial control panels, and address decoding requiring stable component supply in legacy TTL-based designs.

Supply support for SN74LS148D 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 SN74LS148D belongs to TI's legacy 74LS logic family, designed specifically for low-power, high-noise-margin TTL systems operating at 5 V - targeting cost-sensitive, reliability-critical industrial control and instrumentation applications.

FAQ

What is the primary logic function of the SN74LS148D?

The SN74LS148D is an 8-line-to-3-line priority encoder that converts eight active-low data inputs (0–7) into a 3-bit binary output (A0–A2), always selecting the highest-priority (lowest-numbered) asserted input. Its function is defined by the truth table in TI datasheet SDLS053B, with GS and EO flags supporting cascaded configurations. This behavior is fixed in silicon and cannot be reprogrammed.

Does the SN74LS148D support cascading with other priority encoders?

Yes, the SN74LS148D supports hardware cascading using its EI (Enable Input), EO (Enable Output), and GS (Group Select) pins. When multiple SN74LS148D units are connected, EO from a lower-priority stage drives EI of the next stage, allowing seamless expansion to 16-, 24-, or more-line encoding without external logic. The GS output indicates activity in each stage for interrupt prioritization.

What are the absolute maximum ratings for the SN74LS148D supply voltage and operating temperature?

The SN74LS148D has an absolute maximum supply voltage (VCC) of 7 V and an absolute maximum operating free-air temperature range of −65°C to +150°C. However, its recommended operating conditions specify VCC = 4.75 V to 5.25 V and TA = 0°C to 70°C for commercial-grade performance. Exceeding recommended limits may cause timing violations or accelerated aging.

How does the SN74LS148D handle simultaneous low inputs on multiple data lines?

The SN74LS148D resolves simultaneous low inputs using hardwired priority logic: input 0 has highest priority, then 1, 2, ..., up to 7 (lowest). If inputs 2 and 5 are both low, the SN74LS148D outputs the code for input 2 (010) exclusively. This deterministic behavior is inherent to the TTL gate architecture and requires no external arbitration circuitry.

Is the SN74LS148D pin-compatible with newer CMOS logic families like 74HC148?

No, the SN74LS148D is not pin-compatible with 74HC148 or 74HCT148. Although both share identical pin numbering and functional roles (A0–A2, EI, EO, GS, GND, VCC, inputs 0–7), their electrical characteristics differ significantly: SN74LS148D uses bipolar TTL inputs (VIH = 2.0 V, VIL = 0.8 V), while 74HC148 uses CMOS thresholds (VIH ≈ 3.5 V, VIL ≈ 1.5 V at 5 V). Direct substitution risks logic-level incompatibility and undefined states.