Texas Instruments SN74148N3

Overview

SN74148N from Texas Instruments is a TTL 8-line-to-3-line priority encoder IC performing octal binary encoding with active-low inputs and outputs. It features priority decoding to encode the highest-order asserted input (0–7), three encoded binary outputs (A0–A2), group select (GS), and enable in/out (EI/EO) for cascading. It operates at 5 V, delivers 16 mA low-level output drive, and supports keyboard encoding and code conversion in industrial control panels.

For engineers reviewing the SN74148N datasheet, SN74148N pinout, SN74148N application, or SN74148N equivalent, key selection considerations include its active-low logic convention, 10 ns typical propagation delay (tPHL/tPLH), 190 mW typical power dissipation, priority resolution behavior, and compatibility with standard 74-series TTL load requirements.

Technical Context

The SN74148N implements combinational priority encoding using bipolar TTL circuitry, where only the highest-priority active-low input (lowest numeric index) determines the output state. Its internal logic ensures deterministic encoding without race conditions during simultaneous input transitions - though transient glitches on GS may occur during EI assertion when all data inputs are high.

Cascading is enabled via EI (active-low enable input) and EO (active-low enable output), allowing multi-stage expansion without external gates. All eight data inputs (0–7), A0–A2 outputs, GS, and EO are active-low; EI is also active-low. The device requires no external pull-ups for proper TTL interfacing due to built-in input clamping and normalized loading.

Key Specifications

Pinout & Package

SN74148N is supplied in a 16-pin plastic dual in-line package (PDIP-N), 0.300-inch wide body, with standard through-hole mounting and 0.100-inch pin pitch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74148N, SN74LS148N trades speed for power efficiency and noise margin, while SN74HC148N shifts to CMOS operation with broader voltage support but reduced output drive - each addresses distinct system-level trade-offs in legacy upgrade paths.

Availability

SN74148N is available at Aetrix Electronics and suitable for industrial control panels, legacy instrumentation interfaces, and repair programs requiring stable component supply and long-term obsolescence mitigation.

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 manufacturer founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74148N belongs to TI's legacy 74-series TTL logic family, designed specifically for robust, high-noise-margin digital encoding in electromechanical systems and early microprocessor peripheral interfaces.

FAQ

What is the primary function of the SN74148N?

The SN74148N is an 8-line-to-3-line priority encoder that converts up to eight active-low input signals (0–7) into a 3-bit active-low binary output (A0–A2), with priority given to the lowest-numbered asserted input. It also provides group select (GS) and enable in/out (EI/EO) signals for cascading. This function is implemented in standard bipolar TTL technology and is documented in the SDLS053B datasheet.

How does the priority encoding behavior work in the SN74148N?

In the SN74148N, when multiple inputs (0–7) are simultaneously low, only the numerically lowest input determines the output - for example, if both input 2 and input 5 are low, the encoder outputs the binary code for "2". This priority resolution is hardwired in the TTL logic and ensures unambiguous output regardless of input timing skew, as confirmed by the function table in the SN74148N datasheet.

What are the voltage and current specifications for SN74148N inputs and outputs?

The SN74148N operates within a recommended supply range of 4.75 V to 5.25 V. Input thresholds are VIH ≥ 2 V and VIL ≤ 0.8 V. Output drive capability is IOL = 16 mA (low-level sink) and IOH = −800 µA (high-level source). These values are specified under recommended operating conditions in the SN74148N datasheet and define its interoperability with standard TTL logic families.

Can the SN74148N be used in cascaded configurations, and how?

Yes, the SN74148N supports cascading via its EI (enable input) and EO (enable output) pins. EO of a lower-priority stage connects to EI of the next higher-priority stage. When no input is active in the first stage, EO goes high (inactive), enabling the second stage. This allows encoding of more than eight lines - for example, two SN74148N devices can encode 16 lines - as shown in Figure 3 of the SN74148N datasheet.

Is the SN74148N still in active production, and what package options are available?

The SN74148N is an active-production part in the PDIP-N (16-pin plastic DIP) package, with tube packaging (25 units per tube) and RoHS-compliant NiPdAu lead finish. It is listed as "Active" in TI's official packaging addendum, with operating temperature range 0°C to 70°C. Other variants like SN74LS148N and SN74HC148N offer alternative technologies, but SN74148N remains available for legacy system support.