Texas Instruments SN74LS171N

Overview

SN74LS171N from Texas Instruments is a 4-bit synchronous binary counter with dual clock inputs and master reset, fabricated in LS-TTL technology, operating at 5 V supply, with typical propagation delay of 25 ns and fan-out of 20 LSTTL loads, used in digital timing and control logic circuits.

For engineers reviewing the SN74LS171N datasheet, SN74LS171N pinout, SN74LS171N application, or SN74LS171N equivalent, key selection considerations include synchronous counting capability, dual-clock edge sensitivity (CP0/CP1), master reset functionality, TTL-compatible input thresholds, and through-hole DIP-16 packaging for legacy board-level integration.

Technical Context

The SN74LS171N implements a 4-bit synchronous up-counter with parallel load capability, where all four flip-flops are clocked simultaneously by either CP0 (positive-edge) or CP1 (negative-edge), enabling flexible clocking schemes in mixed-edge systems. It features an active-low master reset (MR̄) that asynchronously clears all outputs to zero regardless of clock state.

Count enable is implicit via clock selection and data loading control: parallel data is latched on the selected clock edge only when MR̄ is high and the corresponding clock input is active; no separate enable pin exists. Output decoding requires external logic as the device provides only Q0–Q3 registered outputs without carry or ripple signals.

Key Specifications

Pinout & Package

SN74LS171N is housed in a 16-pin plastic dual in-line package (PDIP) with 0.3-inch body width and standard 0.1-inch pin spacing, designed for wave soldering and socket insertion.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 4-bit synchronous counter applications.

Compared with SN74LS161N and SN74LS191N, the SN74LS171N uniquely provides selectable clock edge sensitivity-enabling direct interface to both rising- and falling-edge sources-while retaining synchronous load and asynchronous reset, making it optimal for legacy system integration where clock polarity is constrained by external hardware.

Availability

SN74LS171N is available at Aetrix Electronics and suitable for industrial control sequencing, test equipment timing, legacy computer peripherals, and educational lab training requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74LS171N 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 logic ICs, with broad legacy product support and military-grade qualification programs.

The SN74LS171N belongs to the 74LS TTL logic family, designed specifically for robust, low-power, medium-speed digital control in commercial and industrial systems where compatibility with established 74xx architectures is essential.

FAQ

What is the primary function of the SN74LS171N?

The SN74LS171N is a 4-bit synchronous binary counter with parallel load capability and dual-clock edge selection (CP0 for rising edge, CP1 for falling edge). It performs deterministic counting or presetting of a 4-bit value on the active clock edge, while supporting asynchronous reset via MR̄. Its core role in circuit design is state progression and address generation in fixed-function digital systems.

Does the SN74LS171N support asynchronous counting?

No, the SN74LS171N does not support asynchronous (ripple) counting. All four internal flip-flops are clocked synchronously by either CP0 or CP1, ensuring simultaneous state updates without propagation delay skew between bits. This eliminates ripple carry glitches and makes the SN74LS171N suitable for applications requiring clean, co-timed output transitions.

Can the SN74LS171N be used as a divide-by-16 counter?

Yes, the SN74LS171N can function as a modulo-16 counter when configured for free-running operation: hold MR̄ high, apply continuous clock pulses to either CP0 or CP1, and allow natural binary progression from 0000 to 1111. After reaching 1111, the next clock cycles back to 0000, delivering a clean 1:16 frequency division with synchronous reset capability.

What is the purpose of the NC pins on the SN74LS171N?

Pins 13 and 14 of the SN74LS171N are designated NC (no connect) and are internally unconnected. They must remain unconnected in PCB layout and should not be tied to V_CC, GND, or any signal. Leaving them floating is acceptable; routing traces or vias to these pins may risk unintended coupling or mechanical interference in dense layouts.

Is the SN74LS171N compatible with modern 3.3 V logic systems?

No, the SN74LS171N is strictly a 5 V-only device with TTL input thresholds and output voltage levels specified for 5 V operation. Interfacing directly with 3.3 V logic risks input overvoltage (due to VIH minimum of 2.0 V but VOH up to 3.4 V under load) and insufficient noise margin. Level translation or buffer isolation is required for safe integration into mixed-voltage systems containing the SN74LS171N.