Texas Instruments SN74LS670NSR

Overview

SN74LS670NSR from Texas Instruments is a 4×4-bit register file with three-state outputs, designed for temporary data storage and addressable read/write operations in TTL-based digital systems. It features 16-word × 4-bit organization, 5.5 V max supply voltage, 35 ns typical access time, and operates across 0°C to 70°C ambient range - used in early microprocessor support logic, ALU register staging, and bus-oriented control units.

For engineers reviewing the SN74LS670NSR datasheet, SN74LS670NSR pinout, SN74LS670NSR application, or SN74LS670NSR equivalent, key selection considerations include its 16-pin SOP (NS) package, TTL-compatible input thresholds, bidirectional data port architecture, and compatibility with LS-family timing and drive requirements in legacy compute and instrumentation designs.

Technical Context

The SN74LS670NSR implements a synchronous, address-decoded 4×4 register file using bipolar TTL circuitry. It supports independent read and write cycles via separate R/W control, uses two address bits (A0, A1) to select one of four 4-bit registers, and employs three-state outputs (OE-controlled) for direct bus interfacing without external buffers.

Its internal architecture includes dual 4-line address decoders, four 4-bit D-type latches with common clock enable, and output-enable-gated bus drivers. All inputs meet standard TTL voltage thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), and outputs drive ±8 mA at V_OL ≤ 0.5 V / V_OH ≥ 2.7 V under nominal conditions.

Key Specifications

Pinout & Package

SOP-16 (NS) package: 10.4 mm × 5.3 mm body, 1.27 mm lead pitch, 2.00 mm max height, gull-wing leads, RoHS-compliant NiPdAu finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS670N and SN74LS670D, the SN74LS670NSR offers identical logic functionality and timing in a space-optimized SOP-16 package with high-volume tape-and-reel delivery - making it optimal for automated SMT production while maintaining full pin and functional compatibility across the SN74LS670 family.

Availability

SN74LS670NSR is available at Aetrix Electronics and suitable for microprocessor support logic, industrial control sequencing, legacy test equipment buffering, and digital signal path staging requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS670NSR 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 ICs, embedded processors, and logic devices with broad industrial, automotive, and consumer applications.

The SN74LS670NSR belongs to TI's legacy 74LS logic family, engineered for high-speed, low-power TTL-compatible digital building blocks in mid-1970s–1990s computing, instrumentation, and control systems.

FAQ

What is the maximum clock frequency supported by the SN74LS670NSR?

The SN74LS670NSR does not specify a maximum clock frequency in its datasheet; instead, it defines timing via access time (35 ns typical) and setup/hold requirements. For reliable operation, the minimum clock period must exceed t_ACC + t_SU + t_H, yielding practical limits near 10–12 MHz in well-designed TTL systems. The SN74LS670NSR relies on edge-triggered behavior rather than continuous clocking, so frequency is constrained by cycle timing margins, not a rated f_MAX.

Does the SN74LS670NSR support simultaneous read and write operations?

No, the SN74LS670NSR does not support true simultaneous read and write. Its R/W pin selects mode: high enables read (outputs driven), low enables write (inputs latched). Attempting concurrent access causes bus contention or undefined data. The SN74LS670NSR requires discrete read and write cycles - each initiated by appropriate R/W state, address, and clock edge - making it unsuitable for dual-port memory applications.

Can the SN74LS670NSR be used with modern 3.3 V logic systems?

The SN74LS670NSR is a 5 V TTL device with input thresholds referenced to 5 V (V_IH ≥ 2.0 V, V_IL ≤ 0.8 V) and outputs swinging near 0 V / 2.7 V. Direct interface with 3.3 V logic risks marginal high-level recognition and excessive input current. To use SN74LS670NSR in mixed-voltage systems, level-shifting buffers or resistor-divider networks are required - the SN74LS670NSR itself provides no 3.3 V compatibility.

What is the function of the R/W pin on the SN74LS670NSR?

The R/W pin on the SN74LS670NSR determines data flow direction: when high, the selected register's contents appear on outputs O0–O3 (read mode); when low, data on I0–I3 is latched into the selected register on the next CLK rising edge (write mode). It is not a true bidirectional control - the SN74LS670NSR uses separate input and output pins, and R/W coordinates which set of paths is active per cycle.

Is the SN74LS670NSR pin-compatible with other members of the 74LS670 family?

Yes, the SN74LS670NSR shares identical pinout and logic functionality with all variants in the SN74LS670 family, including SN74LS670N (PDIP), SN74LS670D (SOIC), and SN74LS670NSR (SOP). All use the same 16-pin configuration, signal naming, and electrical timing - differences are limited to package type, thermal rating, and packaging format. This ensures direct substitution across variants without PCB redesign.