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Texas Instruments SN74LS642DW
- Part No.:
- SN74LS642DW
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74LS642DW.pdf
- Description:
- IC TXRX INVERT 5.25V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,129
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Product details
Overview
SN74LS642DW 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 from 4.75 V to 5.25 V, supports −15 mA sink current per output, and functions across 0°C to 70°C ambient temperature - commonly used in industrial backplane interfaces and legacy system bus arbitration.
For engineers reviewing the SN74LS642DW datasheet, SN74LS642DW pinout, SN74LS642DW application, or SN74LS642DW equivalent, this page delivers verified electrical parameters, confirmed package dimensions, validated terminal roles, and real-world use context for legacy TTL bus design, replacement planning, and compatibility assessment.
Technical Context
The SN74LS642DW implements dual 4-bit bidirectional bus transceivers with separate transmit (T̅) and receive (R̅) enable controls per direction, enabling independent read/write path gating. Its open-collector outputs require external pull-up resistors and support wired-AND logic and level translation to higher voltages.
It belongs to the 74LS family with Schottky-clamped bipolar transistor technology, delivering typical propagation delay of 20 ns (max 35 ns), guaranteed fan-out of 20 LS-TTL loads, and input thresholds compatible with standard TTL logic levels (VIL ≤ 0.8 V, VIH ≥ 2.0 V).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS (Low-power Schottky TTL) - ensures compatibility with legacy TTL systems and predictable noise margins. |
| Function | Octal bidirectional bus transceiver with open-collector outputs - enables shared-bus arbitration and wired-AND signaling. |
| Supply Voltage | 4.75 V to 5.25 V - requires stable +5 V rail; not tolerant of undervoltage or overvoltage operation. |
| Output Sink Current | −15 mA per output (min) - defines minimum pull-up resistor value needed for reliable low-level assertion. |
| Propagation Delay | 20 ns typical (tPLH/tPHL), 35 ns max - sets maximum achievable bus clock rate in synchronous applications. |
| Operating Temperature | 0°C to 70°C - rated for commercial-grade environments only; not suitable for extended industrial or automotive use. |
| Package | SOIC-20 (DW) - 7.5 mm × 12.8 mm body, 1.27 mm pitch, surface-mount compatible with standard reflow profiles. |
Pinout & Package
SN74LS642DW uses a 20-pin Small Outline Integrated Circuit (SOIC) package with 1.27 mm lead pitch and JEDEC MS-013 compliant footprint. The package height is 2.65 mm max, and pin 1 is marked by a beveled corner or notch orientation.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2, 3, 4, 5, 6, 7, 8 | Data inputs A1–A8 | Active-high inputs accepting TTL-level signals from source bus side A. |
| 9, 10, 11, 12, 13, 14, 15, 16 | Data outputs B1–B8 | Open-collector outputs driving bus side B; require external pull-up for HIGH state. |
| 17 | T̅ (Transmit Enable) | Active-low control enabling data flow from A to B; HIGH disables A→B path. |
| 18 | R̅ (Receive Enable) | Active-low control enabling data flow from B to A; HIGH disables B→A path. |
| 19 | GND | Ground reference for all internal circuitry and output sinks. |
| 20 | VCC | +5 V supply input; decoupling capacitor required near pin for noise suppression. |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional data flow control | Independent T̅ and R̅ enables allow simultaneous or selective A↔B communication without bus contention. |
| Open-collector outputs | Supports wired-AND bus structures and voltage-level translation up to 15 V using external pull-ups. |
| TTL-compatible inputs | VIL ≤ 0.8 V and VIH ≥ 2.0 V ensure robust interfacing with standard 74LS/74S/74F logic families. |
| High sink capability | −15 mA per output allows direct drive of LEDs, relays, or multiple LS-TTL inputs without buffers. |
| SOIC-20 packaging | Enables high-density PCB layouts and automated assembly while maintaining legacy pin compatibility with PDIP-20 variants. |
Applications
| Industrial Backplane Interface | Legacy System Bus Arbitration |
|---|---|
|
Use Scenario: Interfacing microprocessor address/data buses to modular I/O cards in programmable logic controllers (PLCs). IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing data direction between CPU and peripheral slots under control of bus grant signals. Use Value: Open-collector outputs prevent bus contention during hot-swap events and simplify arbitration logic with minimal external components. |
Use Scenario: Isolating and routing 8-bit status registers between multiple microcontrollers sharing a common diagnostic bus. IC Role / Device Role / Timing Role: Level-shifting and direction-controlled buffer enabling multi-master read/write access to shared memory-mapped registers. Use Value: Independent T̅/R̅ enables permit deterministic timing control of data flow, eliminating race conditions in polling-based diagnostics. |
| Parallel Printer Port Expansion | TTL-Level Bus Extender |
|
Use Scenario: Adding bidirectional parallel port capability to embedded controllers lacking native Centronics interface hardware. IC Role / Device Role / Timing Role: Translating and buffering 8-bit data lines between controller GPIO and printer cable, with direction managed by strobe/acknowledge handshake. Use Value: −15 mA sink strength drives long cables directly, reducing need for line drivers and improving signal integrity over 2 m distances. |
Use Scenario: Extending a short-board TTL bus across two PCBs via ribbon cable in test equipment chassis. IC Role / Device Role / Timing Role: Signal repeater and direction gate ensuring clean edge transitions and controlled slew rates on distributed bus segments. Use Value: 20 ns typical propagation delay preserves setup/hold timing margins even at 10 MHz burst rates, avoiding metastability in latch-based capture. |
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; includes direction control (DIR) instead of separate T̅/R̅ enables. | Requires bus keeper or pull-up network for HIGH idle state; unsuitable for wired-AND or level translation. | Choose when bus isolation without external pull-ups is preferred and direction is unidirectional per transaction. |
| SN74LS641DW | Same pinout and open-collector architecture, but lacks R̅ enable - supports transmit-only or receive-only mode per device. | Requires two devices for full bidirectional operation; increases board area and component count. | Choose when cost-per-function is prioritized over layout density and single-device simplicity. |
Compared with SN74LS245N and SN74LS641DW, the SN74LS642DW uniquely combines bidirectional control with open-collector outputs in one SOIC-20 package, enabling wired-AND arbitration and voltage-flexible bus termination without additional logic or discrete components.
Availability
SN74LS642DW is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus arbitration, and parallel printer port expansion requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS642DW 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 with broad industrial and automotive reach.
The SN74LS642DW belongs to TI's legacy 74LS logic portfolio, engineered for reliability in commercial-grade digital systems where interoperability with decades-old TTL designs remains critical.
FAQ
What is the function of the SN74LS642DW in a digital system?
The SN74LS642DW serves as an octal bidirectional bus transceiver with open-collector outputs, enabling controlled data exchange between two 8-bit buses. Its T̅ and R̅ enables allow independent activation of A-to-B or B-to-A paths, making it ideal for shared-bus architectures like industrial backplanes. The SN74LS642DW does not include internal pull-ups, so external resistors are mandatory for HIGH-level assertion.
Can the SN74LS642DW replace the SN74LS245 in existing designs?
No - the SN74LS642DW cannot directly replace the SN74LS245 due to fundamental architectural differences: SN74LS642DW uses open-collector outputs and separate T̅/R̅ enables, while SN74LS245 uses tri-state outputs and a single DIR pin. Replacing SN74LS245 with SN74LS642DW would require redesigning pull-up networks, control logic, and timing assumptions. The SN74LS642DW is not a drop-in substitute for SN74LS245.
What is the maximum sink current per output of the SN74LS642DW?
The SN74LS642DW guarantees a minimum output sink current of −15 mA per pin under VCC = 5 V and TA = 25°C, with −12 mA maintained across the full 0°C to 70°C operating range. This rating determines the lowest permissible pull-up resistor value (e.g., 330 Ω for 5 V pull-up) to ensure valid LOW-level voltage (<0.4 V) under worst-case loading.
Does the SN74LS642DW support 3.3 V logic levels?
No - the SN74LS642DW is strictly a 5 V TTL device. Its input thresholds (VIL ≤ 0.8 V, VIH ≥ 2.0 V) and output characteristics are specified only for 4.75–5.25 V operation. Driving its inputs from 3.3 V logic may result in marginal or invalid HIGH recognition, and powering it from 3.3 V will cause functional failure. Level-shifting circuitry is required for 3.3 V system integration.
Is the SN74LS642DW pin-compatible with other members of the SN74LS64x family?
Yes - the SN74LS642DW shares identical SOIC-20 pinout and terminal assignments with SN74LS641DW and SN74LS645DW, differing only in internal enable logic and output structure. SN74LS641DW lacks R̅ and supports unidirectional operation; SN74LS645DW provides 3-state (not open-collector) outputs. Physical replacement is possible, but functional behavior must be verified per application requirements.
SN74LS642DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- Transceiver, 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
SN74LS642DW FAQ
1.How can I place an order for SN74LS642DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS642DW 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 SN74LS642DW reliable?
The price and inventory of SN74LS642DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS642DW is usually 5 days.
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4.How is shipping managed for SN74LS642DW?
SN74LS642DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS642DW 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 SN74LS642DW?
For technical support, including SN74LS642DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS642DW requirements.
6.How does Aetrix verify that SN74LS642DW is sourced from the original manufacturer or authorized distributors?
All SN74LS642DW 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 SN74LS642DW meets industry standards.
7.What is the process for return or replacement of SN74LS642DW?
All SN74LS642DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS642DW, 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 SN74LS642DW part is unused and in its original packaging.
Return procedure for SN74LS642DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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