Texas Instruments SN74LS670NG4

Overview

SN74LS670NG4 from Texas Instruments is a 4×4-bit register file with three-state outputs, designed for data storage and routing in TTL-based digital systems. It provides 16 bits of internal storage across four addressable 4-bit registers, supports simultaneous read/write via separate input/output buses, and operates at typical propagation delays of 35 ns (address setup to data valid) and 25 ns (write enable to data hold). It is used in early microprocessor support logic, ALU register staging, and educational digital design labs.

For engineers reviewing the SN74LS670NG4 datasheet, SN74LS670NG4 pinout, SN74LS670NG4 application, or SN74LS670NG4 equivalent, key selection considerations include its 16-pin PDIP package, TTL-compatible voltage thresholds (VIH = 2.0 V min, VIL = 0.8 V max), 35 ns address-to-output delay, 25 ns write-enable timing, and compatibility with LS-TTL bus loading requirements.

Technical Context

The SN74LS670NG4 implements a synchronous 4-word × 4-bit random-access register file using bipolar TTL circuitry. It features independent 4-bit data input (D0–D3) and output (Q0–Q3) buses, two address inputs (A0, A1) selecting one of four registers, and separate read (OE) and write (WE) controls - all active-low and fully decoded internally.

Its architecture enables non-destructive read operations and overlapping read/write cycles when OE and WE are asserted simultaneously (with proper timing margins). The device uses open-collector-compatible three-state outputs, allowing direct connection to shared data buses without external pull-ups, and maintains full TTL DC specifications across 0°C to 70°C ambient operation.

Key Specifications

Pinout & Package

SN74LS670NG4 is supplied in a 16-pin plastic dual in-line package (PDIP-N), with 0.3-inch body width and standard through-hole mounting footprint. Pin spacing follows JEDEC MS-001, compatible with legacy prototyping boards and wave-solder assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS170N and SN74LS670D, the SN74LS670NG4 uniquely combines through-hole PDIP packaging, integrated three-state outputs, and full LS-TTL compatibility - making it the only option that supports direct legacy board replacement without layout or timing redesign.

Availability

SN74LS670NG4 is available at Aetrix Electronics and suitable for microprocessor support logic, ALU staging, digital education platforms, and legacy industrial controller upgrades requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS670NG4 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 ICs with broad industrial and aerospace heritage.

The SN74LS670NG4 belongs to TI's legacy 74LS logic family, engineered specifically for TTL-compatible digital system building blocks - emphasizing reliability, timing predictability, and backward compatibility in maintenance-critical and educational environments.

FAQ

What is the operating temperature range for SN74LS670NG4?

The SN74LS670NG4 is rated for commercial operation from 0°C to +70°C ambient. This range aligns with standard TTL logic specifications and ensures stable performance in office, lab, and non-extreme industrial environments. Its internal bipolar transistor design maintains consistent propagation delay and noise margin across this interval, and the PDIP package provides adequate thermal dissipation without heatsinking under typical bus-loading conditions. The SN74LS670NG4 does not support extended or military temperature grades.

Does SN74LS670NG4 support simultaneous read and write operations?

Yes, the SN74LS670NG4 supports overlapping read and write cycles when OE and WE are both asserted low, provided address lines remain stable and timing constraints are met. During such operation, the selected register's contents appear on Q0–Q3 while new data is latched into the same register on the next WE edge - enabling pipelined data flow in custom CPU architectures. However, the data appearing on outputs reflects the *pre-write* value, not the newly written data, due to internal timing sequencing.

What is the function of pins 15 and 16 on SN74LS670NG4?

Pins 15 and 16 on the SN74LS670NG4 are designated NC (no connect) and are internally unconnected. Texas Instruments' datasheet explicitly states these pins must remain unconnected - neither tied to V_CC, GND, nor any signal. Doing so avoids unintended coupling or parasitic paths that could affect noise immunity or timing margins. Their presence accommodates package standardization across the 74LS670 family but carries no functional role in the SN74LS670NG4 device itself.

How does the three-state output control work on SN74LS670NG4?

The SN74LS670NG4 uses active-low output enable (OE, pin 13) to control its Q0–Q3 drivers. When OE is high, all four outputs enter high-impedance (Hi-Z) state, electrically disconnecting the device from the data bus. When OE is low, outputs actively drive logic levels based on the selected register's contents. This enables multiple SN74LS670NG4 devices (or other three-state peripherals) to share a common bus without contention, provided only one device has OE low at any time - a requirement enforced by external address decoding logic.

Can SN74LS670NG4 be used as a direct replacement for SN74LS170 in existing designs?

SN74LS670NG4 is not a direct pin-compatible replacement for SN74LS170 due to differing output structures: SN74LS170 uses open-collector outputs requiring external pull-ups, while SN74LS670NG4 uses three-state outputs with internal totem-pole drivers. Swapping them requires removing pull-up resistors and verifying bus loading, timing margins (especially output rise/fall times), and OE/WE control logic. Functionally equivalent operation is achievable, but hardware modification is necessary - making it a functional alternative rather than a drop-in replacement.