Texas Instruments SN74AS876NT

Overview

SN74AS876NT from Texas Instruments is a dual 4-bit D-type edge-triggered flip-flop with inverting 3-state outputs, designed as a bus-oriented register for bidirectional data flow control. It features asynchronous preset (PRE) inputs, true bus-structured pinout, 80 MHz max clock frequency, 4.5–5.5 V supply range, and operates from 0°C to 70°C.

For engineers reviewing the SN74AS876NT datasheet, SN74AS876NT pinout, SN74AS876NT application, or SN74AS876NT equivalent, this device serves as a high-speed, inverting bus register with active-low preset and output enable-critical for legacy TTL-compatible system bus buffering, I/O port latching, and synchronous data staging in industrial controllers and test equipment.

Technical Context

This IC implements two independent 4-bit D flip-flop sections, each with separate clock (CLK), preset (PRE), and output-enable (OE) controls. Data is captured on the low-to-high clock transition; PRE low forces all four Q outputs low regardless of clock state.

The 3-state outputs support direct bus driving with bus-structured pinout (Q/D interleaving), enabling compact PCB layout. Output drive strength is ±48 mA (IOL/IOH), and propagation delays are as low as 3 ns (tPLH) under 50 pF load-optimized for AS-series speed-grade TTL compatibility.

Key Specifications

Pinout & Package

SN74AS876NT is supplied in a 24-pin plastic dual-in-line package (DIP), 300-mil width, with standard through-hole footprint and JEDEC MO-058 AA compliance. Pin 1 is marked by notch or dot; pin numbering follows counterclockwise sequence from top-left corner.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual 4-bit bus register applications.

Compared with SN74ALS876A, SN74AS876NT delivers 2.7× higher clock rate and 2× stronger drive, making it suitable for performance-critical upgrades; versus SN74AS874, its inverting outputs eliminate external inverters in negative-logic bus architectures but require verification of downstream input polarity tolerance.

Availability

SN74AS876NT is available at Aetrix Electronics and suitable for industrial PLC I/O modules, legacy test equipment data capture, communications backplane buffering, and embedded instrumentation control bus applications requiring stable component supply and long-lifecycle support.

Supply support for SN74AS876NT 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 global semiconductor leader specializing in analog, embedded processing, and logic solutions, with over 90 years of innovation in industrial, automotive, and communications markets.

The SN74AS876NT belongs to TI's 74AS logic family-designed for high-speed, low-noise, TTL-compatible digital systems where propagation delay, fanout, and noise immunity are critical in legacy and upgrade designs.

FAQ

What logic family does SN74AS876NT belong to, and how does it differ from 74LS or 74ALS variants?

SN74AS876NT is part of the 74AS (Advanced Schottky) logic family. It offers significantly higher speed (80 MHz vs. 30 MHz for 74ALS876A) and stronger output drive (±48 mA vs. ±24 mA) than 74ALS, while maintaining TTL-compatible voltage thresholds. Unlike 74LS, it uses Schottky-clamped bipolar transistors for reduced propagation delay and improved noise immunity-making SN74AS876NT ideal for timing-critical bus register applications where legacy 74LS/74ALS parts fall short.

Does SN74AS876NT support hot insertion or live bus operation?

SN74AS876NT is not explicitly rated for hot insertion. Its absolute maximum input voltage is 7 V, and disabled 3-state outputs tolerate up to 5.5 V, but no bus-hold, power-up sequencing, or Ioff protection is specified. For live bus operation, external series resistors and careful power sequencing are recommended. Always verify bus contention behavior in-system; SN74AS876NT itself provides no built-in hot-swap safeguards.

What is the function of the PRE pin on SN74AS876NT, and how does it interact with the clock?

The PRE (preset) pin on SN74AS876NT is an asynchronous, active-low input that forces all four Q outputs of its associated 4-bit section low-regardless of clock state or data input. When PRE is low, the flip-flop ignores CLK transitions and D inputs. Only when PRE returns high does the section resume normal edge-triggered operation. This behavior is confirmed in the SN74AS876 function table and applies independently to each of the two sections in SN74AS876NT.

Can SN74AS876NT be used as a replacement for SN74ALS876A in an existing design?

SN74AS876NT is pin-compatible and functionally equivalent to SN74ALS876A in the NT package, with identical pinout and logic behavior. However, due to its higher speed (80 MHz vs. 30 MHz), stronger drive (48 mA vs. 24 mA), and increased ICC (up to 160 mA vs. 31 mA), thermal and power delivery must be re-evaluated. Signal integrity may improve, but overshoot/ringing on unterminated lines could increase. SN74AS876NT is a drop-in replacement only if board-level timing, power, and noise margins accommodate AS-series characteristics.

What are the recommended decoupling practices for SN74AS876NT in high-speed operation?

Each SN74AS876NT requires a minimum 0.1 µF ceramic capacitor placed as close as possible between VCC (pin 24) and GND (pin 12), with short, low-inductance traces. For systems with multiple devices, add a bulk 4.7–10 µF tantalum or aluminum electrolytic capacitor per 5–10 ICs near the power entry point. Avoid daisy-chained VCC/GND routing; use star or plane distribution. These practices mitigate switching noise and maintain stable VCC during 48 mA output transitions-critical to achieving SN74AS876NT's specified 3 ns tPLH and preventing ground bounce.