Texas Instruments SN74148N

Overview

SN74148N from Texas Instruments is an 8-line-to-3-line priority encoder IC in a 16-pin PDIP package, performing active-low octal encoding with cascading enable (EI/EO) and group select (GS) outputs. It delivers 15 ns typical propagation delay (tPHL/tPLH), 60 mW typical power dissipation at 5 V, and operates across 0°C to 70°C. It is used in keyboard scan logic and industrial control panels where input prioritization and compact BCD-compatible encoding are required.

For engineers reviewing the SN74148N datasheet, SN74148N pinout, SN74148N application, or SN74148N equivalent, this page provides verified functional specifications, validated pin roles, confirmed TTL-compatible drive capability (IOL = 4 mA, IOH = −400 µA), and two field-tested alternative parts for legacy system maintenance and redesign.

Technical Context

The SN74148N implements combinational priority encoding: only the highest-order active-low input (0–7) determines the 3-bit binary output (A0–A2), while EI enables encoding and GS flags valid output. Its internal TTL circuitry ensures one normalized 74-series load per input and supports direct cascading via EO/GS signals without external gates.

All inputs and outputs operate at active-low logic levels; input thresholds are VIH ≥ 2 V and VIL ≤ 0.8 V, and outputs meet VOH ≥ 2.7 V (IOL = 4 mA) and VOL ≤ 0.4 V (IOH = −400 µA) under recommended conditions (VCC = 4.75–5.25 V, TA = 0–70°C).

Key Specifications

Pinout & Package

SN74148N uses a 16-pin plastic dual in-line package (PDIP-N) with 0.3-inch width and standard through-hole mounting. Pin 1 is marked by a notch or dot; pin numbering follows counterclockwise sequence from top-left when viewed from component side.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74148N, SN74LS148DR and SN74LS148NSR retain identical encoding behavior, timing, and drive strength but differ in package form factor and assembly method - enabling drop-in functional replacement in legacy systems or migration to modern SMT processes without logic redesign.

Availability

SN74148N is available at Aetrix Electronics and suitable for industrial control panels, legacy test equipment refurbishment, and keyboard interface modules requiring stable component supply and long-term obsolescence management.

Supply support for SN74148N 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 for industrial, automotive, and communications markets.

The SN74LS148 product line was developed for TTL-based digital systems requiring deterministic priority resolution in resource-constrained hardware - targeting keyboard encoders, interrupt controllers, and fault-handling logic in 1970s–1990s instrumentation.

FAQ

What is the logic polarity of inputs and outputs on the SN74148N?

The SN74148N uses active-low logic throughout: all eight data inputs (0–7), EI, EO, GS, and the three encoded outputs (A0–A2) assert logic '0' to indicate activation. This matches mechanical switch grounding and open-collector sensor interfaces without inversion logic. The SN74148N datasheet confirms VIH ≥ 2 V and VIL ≤ 0.8 V thresholds, and VOH/ VOL values reflect this negative-true signaling convention.

Can SN74148N be cascaded with another SN74148N to encode 16 inputs?

Yes - the SN74148N supports direct cascading using EI and EO pins: connect the EO of the lower-priority device to the EI of the higher-priority device. When the higher-priority encoder detects no active input, its EO goes high, enabling the lower-priority unit. GS from both units indicates overall validity. This configuration is explicitly validated in the SN74148N application diagrams and requires no external gates or timing compensation.

Is SN74148N compatible with 3.3 V logic systems?

No - the SN74148N is a 5 V TTL device with VCC range 4.75–5.25 V and input thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V) optimized for 5 V operation. Driving its inputs from 3.3 V logic may result in marginal or non-functional VIH margin, and its 5 V outputs exceed absolute maximum ratings of most 3.3 V ICs. Level translation (e.g., TXB0108) is required for interoperability with 3.3 V systems.

What is the purpose of the GS (Group Select) output on SN74148N?

The GS output on SN74148N is an active-low flag that goes low only when EI is low AND at least one of inputs 0–7 is low - indicating a valid encoded output on A0–A2. It prevents downstream logic from acting on undefined states (e.g., all inputs high or EI high). In practice, GS synchronizes latch strobes or enables display drivers, ensuring data capture occurs only during legitimate encoding events.

Does SN74148N require pull-up resistors on its inputs?

No - SN74148N inputs have internal TTL base-drive structures and specified input current (IIL = −0.4 mA typical) that sink current when pulled low. When left unconnected, inputs float toward VCC due to internal bias but are not guaranteed high; TI recommends tying unused inputs to VCC via 1–10 kΩ resistors for predictable operation. External pull-ups are unnecessary and may increase power draw unnecessarily.