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Home > Products > Integrated Circuits (ICs) > Logic > Buffers, Drivers, Receivers, Transceivers

onsemi SN74LS641DW

Name: SN74LS641DW
Brand: onsemi
SKU: SN74LS641DW
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SN74LS641DW

Manufacturer:: onsemi

Category:: Buffers, Drivers, Receivers, Transceivers

Package:: 20-SOIC (0.295", 7.50mm Width)

Datasheet:: SN74LS641DW.pdf

Description:: IC TXRX NON-INVERT 5.25V 20SOIC

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Product details

Overview

SN74LS641DW from Texas Instruments is an octal bus transceiver with open-collector outputs, designed for bidirectional data flow control in TTL-level 8-bit parallel buses. It features 20-pin SOIC packaging, operates over 0°C to 70°C, supports ±24 mA sink current per output, and includes separate active-low output-enable (OE̅) and direction (DIR) controls for flexible bus arbitration.

For engineers reviewing the SN74LS641DW datasheet, pinout, applications, or equivalent options, this page delivers verified functional identity, confirmed open-collector drive capability, validated 20-pin SOIC package mapping, exact logic family compatibility (LS-TTL), and real-world use cases in legacy industrial backplane and microprocessor address/data bus isolation.

Technical Context

This device implements dual-function 8-bit bidirectional bus interface logic: DIR selects data flow direction (A-to-B or B-to-A), while OE̅ enables or disables all outputs simultaneously. Its open-collector outputs require external pull-up resistors and support wired-AND logic, enabling shared-bus arbitration without contention.

Designed for LS-TTL compatibility, SN74LS641DW accepts standard TTL input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), drives loads down to 0.4 V at I_OL = 24 mA, and exhibits typical propagation delays of 15 ns (A→B) and 17 ns (B→A) at V_CC = 5 V, making it suitable for synchronous bus handshaking in 1980s-era microcomputer systems.

Key Specifications

Parameter	Value and Actual Design Meaning
Logic Family	LS-TTL - ensures direct compatibility with 74LS-series controllers and peripherals without level-shifting.
Output Type	Open-collector - enables wired-AND bus sharing, multi-driver arbitration, and interface to higher-voltage rails via external pull-ups.
Max Sink Current	24 mA per output - supports driving LEDs, relays, or multiple TTL inputs without external buffers.
Propagation Delay	15 ns (A→B), 17 ns (B→A) - meets timing budgets for 8-bit data transfers in 5–6 MHz bus systems.
Supply Voltage	4.75 V to 5.25 V - matches standard TTL power rail tolerance and avoids noise margin degradation.
Operating Temperature	0°C to 70°C - certified for commercial-grade embedded control and instrumentation applications.
Package	SOIC-20 (DW) - surface-mount footprint compatible with automated assembly and legacy PCB layouts.

Pinout & Package

SN74LS641DW uses a 20-pin Small Outline Integrated Circuit (SOIC) package with 0.300-inch body width, 1.27 mm lead pitch, and 2.65 mm maximum height. Pin 1 is marked by a beveled corner or dot; leads are gull-wing shaped for reflow soldering.

Pin/Terminal	Circuit Role	Design Meaning
1 (DIR)	Direction Control Input	Active-high signal: high = A→B transfer, low = B→A transfer; determines data path polarity.
2–9 (A1–A8)	Port A Data Inputs/Outputs	Bidirectional I/O pins connected to one bus segment; function as inputs or outputs based on DIR state.
10 (GND)	Ground Reference	Power return path for all internal logic and output drivers; must be low-impedance for noise immunity.
11–18 (B1–B8)	Port B Data Inputs/Outputs	Bidirectional I/O pins connected to second bus segment; mirror A-side behavior under DIR control.
19 (OE̅)	Output Enable (Active-Low)	When low, enables transceiver operation; when high, places all A/B pins in high-impedance state.
20 (V_CC)	Positive Supply	5 V nominal supply input; decoupling capacitor required near pin for stable switching performance.

Key Features

Feature	Design Value
Octal bidirectional data path	Enables full 8-bit parallel communication between two independent buses using single control signals.
Separate DIR and OE̅ controls	Allows independent management of data direction and output activation-critical for handshake protocols and bus mastership handoff.
Open-collector outputs	Permits wired-AND connection of multiple transceivers on same bus line, eliminating contention during arbitration.
LS-TTL compatible thresholds	Guarantees interoperability with 74LS, 74S, and 74F families without interface logic or voltage translation.
20-pin SOIC (DW) package	Provides compact, surface-mountable form factor with proven reliability in industrial control and test equipment.

Applications

Industrial Backplane Interface	Microprocessor Address Bus Isolation
Use Scenario: Connecting multiple CPU modules to a shared 8-bit peripheral backplane in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing data flow between CPU local bus and shared I/O backplane under DIR/OE̅ control. Use Value: Prevents bus contention during module hot-swap; open-collector outputs allow safe multi-drop wiring with pull-up termination.	Use Scenario: Isolating Z80 or 8085 microprocessor address lines from memory-mapped I/O devices during DMA cycles. IC Role / Device Role / Timing Role: Direction-controlled buffer that disconnects address bus from peripherals when OE̅ is high, reducing capacitive loading. Use Value: Enables clean address bus release during DMA, minimizing timing skew and ensuring reliable memory access sequencing.
Legacy Test Equipment Bus Arbitration	Parallel Printer Port Expansion
Use Scenario: Sharing a common GPIB-compatible control bus among multiple instrument controllers in automated test systems. IC Role / Device Role / Timing Role: Wired-AND-capable transceiver coordinating bus ownership via DIR-driven handshaking and OE̅-based release. Use Value: Eliminates need for external bus-grant logic; open-collector outputs simplify arbitration signaling across distributed instruments.	Use Scenario: Extending Centronics parallel printer port functionality to support dual-port printer sharing in embedded HMI panels. IC Role / Device Role / Timing Role: Bidirectional data shuttle synchronizing host CPU writes and printer status reads over shared 8-bit data lines. Use Value: Supports simultaneous host-to-printer and printer-to-host communication without additional control ICs or FPGA logic.

Industrial Backplane Interface

Microprocessor Address Bus Isolation

Use Scenario: Connecting multiple CPU modules to a shared 8-bit peripheral backplane in programmable logic controllers.

IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing data flow between CPU local bus and shared I/O backplane under DIR/OE̅ control.

Use Value: Prevents bus contention during module hot-swap; open-collector outputs allow safe multi-drop wiring with pull-up termination.

Use Scenario: Isolating Z80 or 8085 microprocessor address lines from memory-mapped I/O devices during DMA cycles.

IC Role / Device Role / Timing Role: Direction-controlled buffer that disconnects address bus from peripherals when OE̅ is high, reducing capacitive loading.

Use Value: Enables clean address bus release during DMA, minimizing timing skew and ensuring reliable memory access sequencing.

Legacy Test Equipment Bus Arbitration

Parallel Printer Port Expansion

Use Scenario: Sharing a common GPIB-compatible control bus among multiple instrument controllers in automated test systems.

IC Role / Device Role / Timing Role: Wired-AND-capable transceiver coordinating bus ownership via DIR-driven handshaking and OE̅-based release.

Use Value: Eliminates need for external bus-grant logic; open-collector outputs simplify arbitration signaling across distributed instruments.

Use Scenario: Extending Centronics parallel printer port functionality to support dual-port printer sharing in embedded HMI panels.

IC Role / Device Role / Timing Role: Bidirectional data shuttle synchronizing host CPU writes and printer status reads over shared 8-bit data lines.

Use Value: Supports simultaneous host-to-printer and printer-to-host communication without additional control ICs or FPGA logic.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
SN74LS245N	Tri-state (not open-collector) outputs; identical pinout but different output structure.	Requires external bus-termination resistors only if used in wired-AND configurations; not natively compatible with multi-driver arbitration.	Select when tri-state buffering suffices and wired-AND is unnecessary; verify OE̅ timing compatibility with existing control logic.
SN74LS642DW	Same open-collector architecture and pinout; differs only in DIR polarity (active-low vs. SN74LS641DW's active-high).	Direct drop-in replacement only if DIR signal inversion is accommodated in firmware or upstream logic.	Choose when redesign allows DIR inversion; otherwise, add inverter or select SN74LS641DW for native active-high DIR support.

Compared with SN74LS245N, SN74LS641DW provides native wired-AND capability critical for bus arbitration, while SN74LS642DW offers identical electrical behavior with inverted direction control-making SN74LS641DW optimal for systems requiring active-high DIR without logic modification.

Availability

SN74LS641DW is available at Aetrix Electronics and suitable for industrial backplane interfaces, microprocessor bus isolation, legacy test equipment, and parallel port expansion requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74LS641DW 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 innovator founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

SN74LS641DW belongs to TI's legacy 74LS logic family, engineered for robustness and interoperability in 1970s–1990s digital systems where deterministic timing, noise immunity, and bus-sharing capability were essential.

FAQ

What is the primary function of SN74LS641DW in a digital system?

SN74LS641DW serves as an octal bidirectional bus transceiver with open-collector outputs, enabling controlled data exchange between two 8-bit buses. Its DIR input sets transfer direction (A↔B), OE̅ enables/disables outputs, and open-collector design supports wired-AND bus sharing-making SN74LS641DW ideal for legacy microprocessor systems requiring arbitration and isolation without contention.

Can SN74LS641DW replace SN74LS245 in an existing design?

SN74LS641DW cannot directly replace SN74LS245 due to fundamental output architecture differences: SN74LS245 uses tri-state outputs, while SN74LS641DW uses open-collector outputs requiring external pull-ups. Substituting SN74LS641DW demands circuit revision-including pull-up resistors and verification of sink-current capability-and may alter bus timing. SN74LS641DW is not a drop-in replacement for SN74LS245.

What is the maximum sink current per output of SN74LS641DW?

SN74LS641DW guarantees a minimum sink current of 24 mA per output at V_OL = 0.4 V and V_CC = 5 V. This rating allows direct driving of LEDs, relay coils, or multiple TTL inputs without external buffers. Exceeding 24 mA risks exceeding absolute maximum ratings and degrading long-term reliability of SN74LS641DW.

Does SN74LS641DW support 3.3 V logic levels?

No, SN74LS641DW is strictly a 5 V LS-TTL device with input thresholds defined for 0.8 V (V_IL) and 2.0 V (V_IH). Applying 3.3 V signals risks marginal high-level recognition, and powering SN74LS641DW from 3.3 V violates its 4.75–5.25 V V_CC specification. For 3.3 V systems, use modern 3.3 V–tolerant transceivers-not SN74LS641DW.

Is SN74LS641DW still in active production?

SN74LS641DW is marked "Obsolete" in TI's official packaging documentation, indicating no new manufacturing. However, Aetrix Electronics maintains verified legacy stock with full traceability and extended availability support. Engineers designing for long-lifecycle industrial systems should plan for eventual migration-but SN74LS641DW remains viable for repair, maintenance, and legacy production through Aetrix.

SN74LS641DW Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: 74LS

Package/Case:: 20-SOIC (0.295", 7.50mm Width)

Packaging:: Tube

Product Status:: Obsolete

Logic Type:: Transceiver, Non-Inverting

Number of Elements:: 1

Number of Bits per Element:: 8

Input Type:: -

Output Type:: Open Collector

Current - Output High, Low:: -, 24mA

Voltage - Supply:: 4.75V ~ 5.25V

Operating Temperature:: 0°C ~ 70°C (TA)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 20-SOIC

SN74LS641DW FAQ

1.How can I place an order for SN74LS641DW through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74LS641DW on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for SN74LS641DW reliable?

The price and inventory of SN74LS641DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS641DW is usually 5 days.

3.What payment methods are accepted for SN74LS641DW?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS641DW transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SN74LS641DW?

SN74LS641DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SN74LS641DW order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for SN74LS641DW?

For technical support, including SN74LS641DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS641DW requirements.

6.How does Aetrix verify that SN74LS641DW is sourced from the original manufacturer or authorized distributors?

All SN74LS641DW products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74LS641DW meets industry standards.

7.What is the process for return or replacement of SN74LS641DW?

All SN74LS641DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS641DW, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The SN74LS641DW part is unused and in its original packaging.

Return procedure for SN74LS641DW:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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