Texas Instruments SN74278N

Overview

SN74278N from Texas Instruments is a 4-bit cascable priority register IC used for data selection and priority encoding in TTL-based digital control logic. It features active-low inputs, complementary outputs (Q and Q̅), asynchronous reset, and direct cascade capability via enable/enable-in pins. Typical use includes interrupt request arbitration and multiplexed address/data path prioritization in industrial control panels.

For engineers reviewing the SN74278N datasheet, SN74278N pinout, SN74278N application, or SN74278N equivalent, key selection considerations include its 16-pin PDIP package, TTL-compatible voltage thresholds (VIH = 2 V min, VIL = 0.8 V max), propagation delay of 25 ns typical at VCC = 5 V, and support for daisy-chained priority resolution without external logic.

Technical Context

The SN74278N implements four independent D-type latches with priority encoding logic that resolves multiple simultaneous input assertions into a single highest-priority output. Each bit has dedicated set (S), reset (R), and enable (E) controls, and the cascade function uses E and E̅ terminals to propagate priority status across multiple devices.

It operates strictly in the bipolar TTL domain (VCC = 4.75–5.25 V), requires no external clock, and relies on level-sensitive enable gating rather than edge-triggered behavior. Input hysteresis is not specified; all timing parameters assume nominal 25°C operation and standard TTL load conditions (1 TTL unit load).

Key Specifications

Pinout & Package

SN74278N is supplied in a 16-pin plastic dual in-line package (PDIP) with 0.3-inch body width and standard through-hole mounting footprint.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS278N and 74F278PC, the SN74278N offers the broadest noise margin and highest input hysteresis tolerance-critical for noisy industrial environments-while maintaining full functional and pinout compatibility across all three variants.

Availability

SN74278N is available at Aetrix Electronics and suitable for industrial control panels, legacy computer bus arbitration, and electromechanical priority selection systems requiring stable component supply and long-term obsolescence management.

Supply support for SN74278N 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 SN74278N belongs to TI's legacy 74xx TTL logic family, designed specifically for deterministic priority resolution in hard-wired digital control systems where microcontroller-based arbitration is impractical or unreliable.

FAQ

What is the operating temperature range for the SN74278N?

The SN74278N is rated for commercial temperature operation from 0°C to +70°C. It is not specified for extended industrial (–40°C to +85°C) or military (–55°C to +125°C) ranges. Designs requiring wider ambient operation must verify functionality empirically or select SN54278 (military-grade) instead of SN74278N.

Does the SN74278N require an external clock signal?

No, the SN74278N is a level-sensitive latch-based priority register and does not require any clock input. Its operation depends solely on the states of the enable (E), input (I0–I3), and set (S0–S3) pins. This makes SN74278N ideal for asynchronous event capture in systems lacking a synchronized timing source.

Can multiple SN74278N devices be cascaded, and how is priority maintained across them?

Yes, SN74278N supports direct cascading using the E (enable) and E̅ (enable complement) pins. The highest-priority device asserts E̅ low to disable lower-priority units downstream. Priority order is fixed by physical wiring sequence, and SN74278N maintains deterministic resolution without arbitration logic or software intervention.

What is the fan-out capability of the SN74278N outputs?

The SN74278N provides standard TTL output drive: IOL = 8 mA (sink) and IOH = –0.4 mA (source). This supports a fan-out of up to 10 standard TTL loads per output. For heavier loads or longer traces, external buffer drivers are recommended to maintain signal integrity and timing margins.

Is the SN74278N still in production, and what is its obsolescence status?

The SN74278N is listed as NRND (Not Recommended for New Designs) by Texas Instruments, though active distribution channels and Aetrix Electronics maintain inventory for legacy system repair and long-lifecycle industrial programs. TI continues to support datasheet documentation and quality assurance for remaining stock.