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Texas Instruments SN74LS642-1N
- Part No.:
- SN74LS642-1N
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS642-1N.pdf
- Description:
- IC TXRX INVERT 5.25V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:1,230
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Product details
Overview
SN74LS642-1N 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 8 independent channels, operates at 0°C to 70°C, supports 5 V supply, and delivers typical propagation delay of 20 ns (A→B) and 22 ns (B→A). It is used in legacy industrial backplane interfaces and microprocessor system address/data bus isolation.
For engineers reviewing the SN74LS642-1N datasheet, SN74LS642-1N pinout, SN74LS642-1N application, or SN74LS642-1N equivalent, key selection criteria include open-collector output compatibility with wired-AND logic, 5 V TTL voltage levels, 20-pin PDIP package constraints, and timing behavior under capacitive loading up to 15 pF.
Technical Context
The SN74LS642-1N implements dual 4-bit bidirectional bus transceivers with separate A- and B-side I/Os and active-low direction (DIR) and output-enable (OE) controls. Each channel uses open-collector NPN output stages, requiring external pull-up resistors for logic HIGH assertion.
It belongs to the 74LS family and maintains standard TTL input thresholds (VIL ≤ 0.8 V, VIH ≥ 2.0 V), fan-out capability of 20 LS-TTL loads, and output sink current rating of 24 mA per pin - enabling direct interface with multiple downstream TTL inputs or discrete LED indicators.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS (Low-power Schottky TTL), ensuring compatibility with legacy 5 V TTL systems and predictable noise margins. |
| Function | Octal bidirectional bus transceiver with open-collector outputs, supporting wired-AND bus arbitration and level translation via external pull-ups. |
| Supply Voltage | 5 V ±5%, defining strict requirement for regulated 5 V rail - no operation outside 4.75–5.25 V range. |
| Propagation Delay | 20 ns (A→B), 22 ns (B→A) at VCC = 5 V, CL = 15 pF, establishing maximum achievable bus cycle rate (~20 MHz worst-case). |
| Output Sink Current | 24 mA per pin (min), enabling direct drive of LEDs or multiple LS-TTL inputs without buffer amplification. |
| Operating Temperature | 0°C to 70°C, confirming commercial-grade qualification suitable for non-military, non-automotive indoor equipment. |
| Package | 20-pin PDIP (N), 0.3-inch width, through-hole mounting compatible with standard 0.1-inch grid prototyping and legacy PCB assembly. |
Pinout & Package
SN74LS642-1N is housed in a 20-pin plastic dual in-line package (PDIP-N) with 0.3-inch body width and standard 0.1-inch lead pitch. Pin 1 is marked by a notch or dot; leads are tin-lead (NIPDAU) finish, RoHS-compliant.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Active-HIGH signal determining data flow: HIGH = A→B, LOW = B→A; must be stable before data transfer. |
| 2–9 (A1–A8) | Side-A I/O Terminals | Open-collector outputs/inputs on A bus; require external pull-up for HIGH logic; tolerate floating states during high-impedance mode. |
| 10 (GND) | Ground Reference | Primary 0 V return path for all internal circuitry and output sinks; must be low-impedance connection to minimize ground bounce. |
| 11–18 (B1–B8) | Side-B I/O Terminals | Open-collector outputs/inputs on B bus; electrically identical to A-side pins; enable bidirectional wired-AND bus sharing. |
| 19 (OE) | Output Enable Input | Active-LOW control: LOW enables transceiver function, HIGH forces all outputs into high-impedance state - critical for bus contention avoidance. |
| 20 (VCC) | Power Supply | +5 V DC input; requires local 0.1 µF ceramic decoupling capacitor placed within 1 cm of pin to suppress switching noise. |
Key Features
| Feature | Design Value |
|---|---|
| Open-collector outputs | Enable wired-AND bus topology, multi-driver arbitration, and simple level shifting using external pull-up resistors to 3.3 V or 5 V. |
| Bidirectional data path | Single DIR pin configures full 8-bit data flow direction, reducing control line count versus unidirectional transceivers. |
| High sink current (24 mA) | Drives LEDs directly or fans out to ≥20 LS-TTL loads without external buffers - simplifies board-level logic design. |
| Standard 74LS timing | Guaranteed 22 ns max propagation delay ensures interoperability with other 74LS devices in synchronous bus systems. |
| 20-pin PDIP package | Supports hand-soldering, socket-based prototyping, and legacy automated insertion - ideal for repair, test, and low-volume industrial builds. |
Applications
| Microprocessor System Bus Isolation | Legacy Industrial Backplane Interface |
|---|---|
Use Scenario: Isolating CPU address/data bus from peripheral expansion slots in 8-bit embedded controllers. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing data flow between Z80/8085 CPU and memory-mapped peripherals with open-collector arbitration. Use Value: Prevents bus contention during DMA or interrupt-driven transfers via OE-controlled high-Z states and DIR-synchronized direction switching. | Use Scenario: Interfacing multiple PLC I/O modules over shared parallel backplane wiring. IC Role / Device Role / Timing Role: Open-collector transceiver enabling wired-AND fault signaling and multi-drop data exchange across 8-bit parallel bus segments. Use Value: Allows any module to assert status flags (e.g., fault, ready) simultaneously without hardware OR gates - reducing component count and layout complexity. |
| LED Status Array Driver | TTL-Level Logic Level Shifter |
Use Scenario: Driving 8 discrete panel-mounted LEDs from microcontroller GPIO lines with current sinking capability. IC Role / Device Role / Timing Role: Output driver converting logic-level signals into 24 mA sink paths for common-anode LED arrays. Use Value: Eliminates need for discrete transistor drivers; leverages built-in 24 mA sink rating to achieve full brightness without external components. | Use Scenario: Translating 5 V TTL logic to 3.3 V or 2.5 V logic domains using external pull-up resistors. IC Role / Device Role / Timing Role: Level-shifting transceiver where pull-ups connect to lower-voltage rail while SN74LS642-1N provides controlled sinking. Use Value: Achieves safe, noise-immune interfacing between mixed-voltage subsystems without dedicated level-shift ICs or complex bias networks. |
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 output inversion option; same 20-pin PDIP package. | Requires bus keeper or pull-ups only for floating-state termination; not suitable for wired-AND or multi-driver arbitration. | Select when tri-state bus sharing suffices and open-collector functionality is unnecessary. |
| SN74LS641-1N | Identical pinout and open-collector architecture; differs only in DIR polarity (active-LOW vs. SN74LS642-1N's active-HIGH). | Requires inverted direction control signal; otherwise drop-in compatible in existing layouts with minor logic adjustment. | Select when system-level DIR signal is active-LOW and board revision is constrained. |
Compared with SN74LS245N, SN74LS642-1N enables wired-AND bus structures and higher sink current; compared with SN74LS641-1N, it simplifies direction control logic by eliminating external inversion but mandates matching DIR polarity in firmware/hardware.
Availability
SN74LS642-1N is available at Aetrix Electronics and suitable for legacy industrial control upgrades, microprocessor development systems, and repair of discontinued instrumentation requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74LS642-1N 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic products with broad industrial and automotive reach.
The SN74LS642-1N belongs to TI's legacy 74LS logic family, engineered for robustness in 5 V TTL systems and designed specifically for bidirectional data routing in resource-constrained industrial and computing platforms.
FAQ
What is the maximum capacitive load SN74LS642-1N can drive reliably?
The SN74LS642-1N is characterized for operation with up to 15 pF total load capacitance per output, including PCB trace and input capacitance of downstream devices. Exceeding this value increases propagation delay and may cause marginal timing in high-speed bus applications. For loads >15 pF, consider adding series resistance or using a buffer stage. The SN74LS642-1N datasheet specifies timing parameters only under 15 pF conditions.
Does SN74LS642-1N support hot-swapping or live insertion?
No, SN74LS642-1N does not support hot-swapping. Its 74LS architecture lacks power-up/down protection, bus-hold, or IOFF circuitry. Inserting or removing SN74LS642-1N while powered risks latch-up, transient overstress, or data corruption on shared buses. Always power down the system before replacing SN74LS642-1N in socketed applications.
Can SN74LS642-1N be used with 3.3 V logic systems?
SN74LS642-1N requires a 5 V supply and is not 3.3 V tolerant on inputs or outputs. However, its open-collector outputs can interface with 3.3 V systems by connecting external pull-up resistors to 3.3 V - provided input thresholds of downstream 3.3 V receivers accept 5 V-tolerant or LVTTL-compatible levels. Do not apply 3.3 V to VCC or expect guaranteed operation below 4.75 V.
What is the difference between SN74LS642-1N and SN74LS642N?
SN74LS642-1N denotes the version with updated characterization and tighter AC timing specifications per the March 1988 revision of SDLS189, while SN74LS642N refers to earlier revisions. Both share identical pinout, DC specs, and package. The "-1" suffix indicates improved propagation delay consistency and enhanced output drive stability - critical for timing-critical bus designs where margin is constrained.
Is SN74LS642-1N RoHS compliant?
Yes, SN74LS642-1N is RoHS compliant, with lead finish specified as NiPdAu (NIPDAU) and full compliance documented in TI's Package Option Addendum. It contains no lead, mercury, cadmium, hexavalent chromium, PBB, or PBDE above threshold limits, meeting EU Directive 2011/65/EU requirements for sale in restricted markets.
SN74LS642-1N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-DIP (0.300", 7.62mm)
- 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:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74LS642-1N FAQ
1.How can I place an order for SN74LS642-1N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS642-1N 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 SN74LS642-1N reliable?
The price and inventory of SN74LS642-1N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS642-1N is usually 5 days.
3.What payment methods are accepted for SN74LS642-1N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS642-1N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS642-1N?
SN74LS642-1N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS642-1N 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 SN74LS642-1N?
For technical support, including SN74LS642-1N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS642-1N requirements.
6.How does Aetrix verify that SN74LS642-1N is sourced from the original manufacturer or authorized distributors?
All SN74LS642-1N 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 SN74LS642-1N meets industry standards.
7.What is the process for return or replacement of SN74LS642-1N?
All SN74LS642-1N units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS642-1N, 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 SN74LS642-1N part is unused and in its original packaging.
Return procedure for SN74LS642-1N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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