Texas Instruments SN74LS641-1N

Overview

SN74LS641-1N from Texas Instruments is an octal bus transceiver with open-collector outputs, designed for bidirectional data transmission in TTL-level systems. It features 8-bit non-inverting data paths, independent output-enable control per direction, and supports wired-AND bus interfacing. It operates across 0°C to 70°C and is packaged in a 20-pin PDIP for through-hole prototyping and industrial control backplanes.

For engineers reviewing the SN74LS641-1N datasheet, SN74LS641-1N pinout, SN74LS641-1N application, or SN74LS641-1N equivalent, key selection criteria include open-collector drive capability, TTL-compatible input thresholds, directional enable logic timing, and compatibility with legacy 74LS bus architectures in industrial I/O modules and instrumentation interfaces.

Technical Context

The SN74LS641-1N implements dual 4-bit bidirectional transceivers in a single 20-pin package, with separate A→B and B→A data paths each controlled by dedicated output-enable (OE) inputs. Its open-collector outputs allow direct wired-OR/WIRED-AND bus termination without external pull-ups on shared lines.

It uses standard 74LS bipolar transistor–transistor logic, delivering typical propagation delays of 15 ns (A→B) and 16 ns (B→A) at V_CC = 5 V, with guaranteed high-level output voltage ≥2.7 V and low-level output voltage ≤0.5 V under 4.8-mA sink load - enabling robust noise margin in noisy industrial environments.

Key Specifications

Pinout & Package

SN74LS641-1N is housed in a 20-pin plastic dual in-line package (PDIP) with 0.3-inch body width and standard 0.1-inch pin pitch. Pin 1 is marked by a notch or dot; pins are numbered counter-clockwise from top-left corner when viewed from component side.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal bus transceiver applications.

Compared with SN74LS245N and SN74LS642-1N, the SN74LS641-1N uniquely delivers non-inverting octal bidirectional transfer with per-direction enable and open-collector outputs - making it irreplaceable in legacy wired-AND bus topologies requiring independent control of data flow direction without signal inversion.

Availability

SN74LS641-1N is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy instrumentation buses, programmable logic controller I/O expansion, automated test equipment fixture control, and embedded system bus bridging requiring stable component supply across extended production lifecycles.

Supply support for SN74LS641-1N 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 founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74LS641-1N belongs to TI's legacy 74LS logic family, engineered for reliability and interoperability in industrial control, test equipment, and military-grade systems where long-term component availability and deterministic timing are critical.

FAQ

What is the function of the SN74LS641-1N in a digital system?

The SN74LS641-1N serves as an octal bidirectional bus transceiver with open-collector outputs, enabling controlled data exchange between two 8-bit parallel buses. It supports independent A→B and B→A data paths via dedicated output-enable inputs, and its open-collector design allows wired-AND bus configurations essential in legacy industrial and instrumentation systems. The SN74LS641-1N maintains strict TTL voltage thresholds and timing for seamless integration into 74LS-based architectures.

Does the SN74LS641-1N require external pull-up resistors?

Yes, the SN74LS641-1N requires external pull-up resistors on all A-side and B-side data lines because its outputs are open-collector. Without pull-ups, outputs cannot assert a HIGH logic level. Typical values range from 1.8 kΩ to 10 kΩ depending on bus capacitance and speed requirements. The SN74LS641-1N datasheet specifies minimum sink current (4.8 mA) and maximum low-level voltage (0.5 V), guiding proper resistor selection to maintain noise margin and timing integrity.

Can the SN74LS641-1N be used as a direct replacement for SN74LS245N?

No, the SN74LS641-1N is not a direct replacement for SN74LS245N due to fundamental architectural differences: SN74LS641-1N has open-collector outputs and independent directional enables, whereas SN74LS245N uses tri-state outputs with a single bidirectional OE. Substituting them requires redesigning bus termination (adding pull-ups), revising enable logic, and verifying timing margins. The SN74LS641-1N also lacks the direction-control (DIR) pin found on SN74LS245N, making pin-to-pin replacement impossible without PCB modification.

What is the maximum sink current per output of the SN74LS641-1N?

The SN74LS641-1N guarantees a minimum sink current of 4.8 mA per output while maintaining V_OL ≤ 0.5 V at V_CC = 5 V and T_A = 25°C. This rating ensures reliable driving of multiple TTL inputs or moderate capacitive loads (e.g., 50–100 pF per line). Exceeding this current may cause V_OL to rise above specification, degrading noise immunity. The SN74LS641-1N does not specify source current capability since its outputs are open-collector and cannot actively drive HIGH.

Is the SN74LS641-1N RoHS compliant?

Yes, the SN74LS641-1N is RoHS compliant, as confirmed by Texas Instruments' packaging addendum: lead finish is NiPdAu (NIPDAU), and RoHS status is marked "Yes" for all active PDIP variants including SN74LS641-1N and SN74LS641-1N.A. This compliance applies to the lead finish and homogeneous materials per EU Directive 2011/65/EU, with no exemptions claimed. The SN74LS641-1N meets JEDEC J-STD-609A Class 1 marking requirements and is suitable for use in environmentally regulated commercial electronics.