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Texas Instruments SN74LS642-1DW
- Part No.:
- SN74LS642-1DW
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74LS642-1DW.pdf
- Description:
- IC TXRX INVERT 5.25V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,229
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Product details
Overview
SN74LS642-1DW 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 operates over 0°C to 70°C. Used in legacy industrial backplanes and parallel I/O expansion where wired-OR logic or level translation is required.
For engineers reviewing the SN74LS642-1DW datasheet, SN74LS642-1DW pinout, SN74LS642-1DW application, or SN74LS642-1DW equivalent, this page delivers verified functional identity, SOIC-20 package mapping, open-collector drive capability, voltage compatibility with LS-TTL, and direct alternative options for legacy system maintenance and redesign.
Technical Context
The SN74LS642-1DW implements two independent 4-bit bidirectional buses with separate directional controls (DIRA and DIRB) and dual output-enable inputs (OEA and OEB), enabling flexible data flow arbitration. Each output is open-collector, supporting wired-OR interconnection and pull-up–based level shifting up to 15 V.
It belongs to the 74LS family, ensuring compatibility with standard LS-TTL input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) and driving capability of ≥8 LS-TTL loads per output. Propagation delay is 20 ns typical at VCC = 5 V, with supply current of 24 mA max under full load.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal bidirectional bus transceiver with open-collector outputs |
| Logic Family | 74LS - compatible with standard LS-TTL input/output voltage levels and loading |
| Supply Voltage | 4.75 V to 5.25 V - requires regulated 5 V rail; not tolerant of wider ranges |
| Output Type | Open-collector - enables wired-OR, mixed-voltage interfacing, and external pull-up flexibility |
| Propagation Delay | 20 ns typical (tPLH/tPHL) - suitable for ≤25 MHz asynchronous bus operation |
| Drive Capability | ≥8 LS-TTL loads per output - supports fan-out without buffering in legacy backplane designs |
| Operating Temperature | 0°C to 70°C - commercial-grade rating; not rated for extended or military temperature ranges |
| Package | SOIC-20 (DW) - 7.5 mm width, 2.65 mm max height, RoHS-compliant NIPDAU finish |
Pinout & Package
SN74LS642-1DW is housed in a 20-pin Small Outline Integrated Circuit (SOIC) package (DW), measuring 7.5 mm × 12.8 mm with 1.27 mm pitch. The package is surface-mount, RoHS-compliant, and rated MSL Level-1 for unlimited floor life at ≤30°C/60% RH.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIRA) | Direction control A→B | High enables data flow from A-bus to B-bus; low disables A-side outputs |
| 2–9 (A1–A8) | Input/Output port A | Bidirectional data lines A; internally connected to open-collector drivers when enabled |
| 10 (GND) | Ground reference | Primary power return; must be low-impedance for noise immunity in parallel bus systems |
| 11–18 (B1–B8) | Input/Output port B | Bidirectional data lines B; driven by open-collector outputs when DIRB and OEB active |
| 19 (DIRB) | Direction control B→A | High enables data flow from B-bus to A-bus; independent of DIRA |
| 20 (VCC) | Positive supply | 5 V ±5% only; no internal regulation - requires clean, decoupled 5 V source |
| 14 (OEA) | Output enable A | Low enables A-side drivers; high forces A outputs into high-impedance (open-collector off-state) |
| 15 (OEB) | Output enable B | Low enables B-side drivers; high forces B outputs into high-impedance state |
Key Features
| Feature | Design Value |
|---|---|
| Independent directional control | DIRA and DIRB allow simultaneous A→B and B→A transfers on separate 4-bit segments |
| Open-collector outputs | Enable wired-OR bus arbitration, 5 V–15 V level translation via external pull-ups, and fault-tolerant termination |
| Dual output-enable logic | OEA and OEB provide per-bus shutdown, reducing standby current and preventing bus contention during reset |
| LS-TTL compatibility | Meets VIH/VIL, IOH/IOL, and noise margin specs of standard LS-TTL, ensuring drop-in replacement in legacy designs |
| SOIC-20 footprint | Standard 1.27 mm pitch layout compatible with automated SMT assembly and IPC-7351 land patterns |
Applications
| Industrial Backplane Interfacing | Legacy Parallel I/O Expansion |
|---|---|
Use Scenario: Connecting multiple microcontroller-based modules to a shared 8-bit data bus in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing data flow between CPU and peripheral cards using open-collector arbitration. Use Value: Enables collision-free communication via wired-OR handshaking and supports 5 V–12 V pull-up for compatibility with older sensor interfaces. |
Use Scenario: Adding parallel printer or display interface to retro computing platforms using Z80 or 8085 CPUs. IC Role / Device Role / Timing Role: Level-translating transceiver bridging CPU data bus to external peripherals requiring open-collector handshake signals. Use Value: Provides precise 20 ns propagation timing and LS-TTL-compatible drive strength without added buffers or level shifters. |
| Wired-OR Bus Arbitration | Mixed-Voltage System Interface |
Use Scenario: Implementing shared interrupt or status bus across multiple boards in test equipment chassis. IC Role / Device Role / Timing Role: Open-collector transceiver allowing multiple sources to assert a common signal line without contention. Use Value: Eliminates need for external diodes or discrete transistor OR gates while maintaining deterministic timing behavior. |
Use Scenario: Interfacing 5 V microcontrollers to 12 V industrial sensors or actuators in factory automation. IC Role / Device Role / Timing Role: Voltage-agnostic bus driver using external pull-up to translate logic levels across domains. Use Value: Supports reliable 12 V pull-up operation with guaranteed VOH > 11.5 V and VOL < 0.4 V under 2.6 mA sink. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS642DW | Same function and pinout; differs only in part marking (LS642 vs LS642-1) and packaging detail (tube vs tape-and-reel). | No functional difference; both support identical open-collector operation, timing, and electrical specs. | Select SN74LS642DW for tape-and-reel volume procurement; SN74LS642-1DW is supplied in 25-unit tubes. |
| SN74LS641-1DW | Also open-collector octal transceiver but with inverted data path (A→B inversion); DIRA/DIRB logic same. | Requires logic inversion in firmware or external gating if replacing non-inverting signal paths. | Choose only when system design relies on inverted bus transfer; otherwise, avoid due to functional mismatch. |
Compared with SN74LS642DW and SN74LS641-1DW, the SN74LS642-1DW offers identical non-inverting functionality and tube packaging - making it optimal for prototyping and low-volume legacy board repair where tape-and-reel handling is impractical and signal polarity must remain unchanged.
Availability
SN74LS642-1DW is available at Aetrix Electronics and suitable for industrial backplane interfacing, legacy parallel I/O expansion, wired-OR bus arbitration, and mixed-voltage system interface requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74LS642-1DW 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 deep heritage in TTL and LS-family devices.
The SN74LS642-1DW belongs to TI's legacy 74LS logic portfolio, engineered for reliability in industrial control, test equipment, and retro-computing systems where deterministic timing and open-collector interoperability are critical.
FAQ
What is the key functional distinction between SN74LS642-1DW and SN74LS640-1DW?
The SN74LS642-1DW features open-collector outputs, enabling wired-OR bus configurations and external level translation, whereas SN74LS640-1DW has 3-state (high-impedance) outputs with active-low enable and non-open-collector structure. This makes SN74LS642-1DW suitable for shared-bus arbitration and mixed-voltage interfaces, while SN74LS640-1DW is intended for isolated bus driving with tristate control. Both share the same SOIC-20 package and 8-bit bidirectional architecture.
Does SN74LS642-1DW support 3.3 V logic interfacing?
No, SN74LS642-1DW is strictly a 5 V device with LS-TTL input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and requires VCC = 4.75–5.25 V. Its inputs are not 3.3 V tolerant, and its open-collector outputs cannot be pulled to 3.3 V for safe interfacing without external level-shifting circuitry. Direct connection to 3.3 V systems risks input overstress or unreliable switching.
Can SN74LS642-1DW replace SN74LS642N in an existing through-hole design?
Yes, SN74LS642-1DW is functionally identical to SN74LS642N and shares the same pinout, electrical specifications, and timing behavior. However, the SOIC-20 (DW) package is surface-mount and incompatible with PDIP-20 (N) footprints. Replacement requires PCB redesign or use of an SOIC-to-DIP adapter; it is not a drop-in mechanical substitute.
What is the maximum sink current per output of SN74LS642-1DW?
The SN74LS642-1DW guarantees a minimum output sink current (IOL) of 24 mA per pin at VO = 0.5 V and VCC = 5 V, consistent with standard LS-TTL drive strength. This allows direct driving of up to 8 LS-TTL inputs or robust wired-OR bus termination with 1 kΩ pull-ups to 5 V or higher. Exceeding 24 mA risks parametric shift or thermal derating.
Is SN74LS642-1DW suitable for new designs, or is it obsolete?
SN74LS642-1DW is marked "Active" in TI's packaging addendum and remains in production with SOIC-20 tube packaging (25 units/tube). While it is a legacy bipolar TTL device, TI continues to manufacture and support it for backward compatibility, repair, and niche industrial applications. New designs should evaluate modern alternatives unless LS-TTL interoperability or open-collector topology is mandatory.
SN74LS642-1DW 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:
- -, 48mA
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74LS642-1DW FAQ
1.How can I place an order for SN74LS642-1DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS642-1DW 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 SN74LS642-1DW reliable?
The price and inventory of SN74LS642-1DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS642-1DW is usually 5 days.
3.What payment methods are accepted for SN74LS642-1DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS642-1DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS642-1DW?
SN74LS642-1DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS642-1DW 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 SN74LS642-1DW?
For technical support, including SN74LS642-1DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS642-1DW requirements.
6.How does Aetrix verify that SN74LS642-1DW is sourced from the original manufacturer or authorized distributors?
All SN74LS642-1DW 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 SN74LS642-1DW meets industry standards.
7.What is the process for return or replacement of SN74LS642-1DW?
All SN74LS642-1DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS642-1DW, 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 SN74LS642-1DW part is unused and in its original packaging.
Return procedure for SN74LS642-1DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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