Texas Instruments SN54LS670J

Overview

SN54LS670J from Texas Instruments is a military-grade 4×4 register file IC with three-state outputs, designed for synchronous data storage and selective read/write operations in TTL-based control logic and early microprocessor support systems. It provides 16-bit total storage (four 4-bit words), operates over –55°C to +125°C, supports dual address decoding (A0/A1), and features independent write-enable (WE) and output-enable (OE) controls for bus isolation.

For engineers reviewing the SN54LS670J datasheet, SN54LS670J pinout, SN54LS670J application, or SN54LS670J equivalent, this device is critical for legacy aerospace avionics, test equipment sequencers, and discrete CPU datapath designs requiring deterministic 4-bit word access with bus contention avoidance.

Technical Context

The SN54LS670J implements a fully decoded 2-bit address space (A0, A1) selecting one of four 4-bit registers for simultaneous read or write. Its internal architecture uses edge-triggered latches synchronized to the rising edge of WE, with separate OE control enabling high-impedance output states without affecting internal storage.

Designed for direct interface with LS-TTL buses, it features guaranteed 3.5-V minimum VOH at IOL = 8 mA and VIH = 2.0 V threshold, with propagation delays under 35 ns (tPLH/tPHL) across full military temperature range. Input clamping diodes and output current limiting ensure robustness in noisy embedded environments.

Key Specifications

Pinout & Package

SN54LS670J is housed in a 16-pin Ceramic Dual In-line Package (CDIP-J), hermetically sealed for high-reliability operation in harsh environments. The package meets MIL-STD-883 requirements and features tin-lead (SNPB) leads with no moisture sensitivity rating (N/A for Pkg Type).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS670N and SNJ54LS670W, the SN54LS670J offers through-hole CDIP reliability and legacy repairability for field-maintainable military systems, while retaining identical logic functionality and timing behavior across all three variants.

Availability

SN54LS670J is available at Aetrix Electronics and suitable for avionics subsystems, industrial control sequencers, and legacy test equipment requiring stable component supply and long-term obsolescence management.

Supply support for SN54LS670J 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 high-reliability logic solutions for aerospace, defense, and industrial markets.

The SN54LS670J belongs to TI's military 54LS logic family, engineered for deterministic timing, radiation-hardened operation, and compatibility with legacy TTL system architectures deployed in safety-critical infrastructure.

FAQ

What is the function of the NC pins on the SN54LS670J?

Pin 15 and Pin 16 of the SN54LS670J are designated No Connect (NC) and must remain unconnected in circuit design. TI documentation explicitly states these pins are internally unused and electrically isolated; connecting them risks parasitic coupling or undefined behavior. The SN54LS670J datasheet confirms NC pins serve no functional role and require no termination or grounding-this applies strictly to the SN54LS670J and differs from some later register file variants.

Does the SN54LS670J support simultaneous read and write operations?

No, the SN54LS670J does not support true simultaneous read and write. While OE and WE are independent controls, writing to a register (via WE high) and reading from the same register (via OE low) in the same cycle causes bus contention because the outputs reflect the *pre-write* state until the next WE edge. The SN54LS670J datasheet specifies that reliable operation requires sequential access: write first, then read after propagation delay. This limitation is inherent to its latch-based architecture and applies identically to the SN54LS670J.

What is the maximum clock frequency implied by the SN54LS670J's timing specifications?

The SN54LS670J has no internal clock; its operation is asynchronous and edge-triggered on WE. The maximum effective cycle rate is determined by tW (minimum WE pulse width = 20 ns), tS (setup time = 20 ns), and tH (hold time = 10 ns), yielding a minimum cycle time of ~75 ns-or approximately 13 MHz maximum sustained access rate. This value is derived directly from SDLS193 timing tables and applies specifically to the SN54LS670J under worst-case military temperature conditions.

Can the SN54LS670J be used with modern 3.3-V systems?

No, the SN54LS670J is strictly a 5-V TTL device and is not 3.3-V compatible. Its absolute maximum VCC is 5.5 V, VIH minimum is 2.0 V, and it draws significant current (ICC = 60 mA typical) incompatible with 3.3-V rail budgets. Interfacing with 3.3-V logic requires level-shifting buffers; direct connection risks damage or metastability. This constraint is documented in the SN54LS670J electrical characteristics table and applies uniformly across all CDIP-J packaged units.

How does the SN54LS670J differ from the SN74LS670 in terms of internal circuitry?

The SN54LS670J and SN74LS670 share identical logic design, pinout, and functional behavior-their internal circuitry is functionally equivalent. Differences are limited to process qualification (MIL-PRF-38535 Class B vs. commercial), temperature grading (–55°C to +125°C vs. 0°C to +70°C), packaging (hermetic CDIP-J vs. plastic PDIP-N), and reliability testing. TI's SDLS193 datasheet confirms no architectural or parametric divergence exists between SN54LS670J and SN74LS670 beyond these manufacturing and environmental specifications.