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Texas Instruments SN74LS642NSR
- Part No.:
- SN74LS642NSR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74LS642NSR.pdf
- Description:
- IC TRANSCEIVER INVERT 5.25V 20SO
- Quantity:
- Payment:
- Shipping:
Inventory:4,234
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Product details
Overview
SN74LS642NSR 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 (OE) and direction (DIR) controls, and operates over 0°C to 70°C. Used in legacy industrial control backplanes and parallel I/O expansion interfaces where wired-OR logic or level translation is required.
For engineers reviewing the SN74LS642NSR datasheet, SN74LS642NSR pinout, SN74LS642NSR application, or SN74LS642NSR equivalent, key selection criteria include open-collector drive capability, TTL-compatible input thresholds, 20-pin SOP package compatibility, and support for wired-OR bus arbitration in legacy parallel architectures.
Technical Context
The SN74LS642NSR implements two independent 4-bit bidirectional transceivers within a single 20-pin SOP package. Each 4-bit section has dedicated DIR and OE inputs, enabling selective direction control per nibble without external logic. Its open-collector outputs allow direct connection to shared buses with pull-up resistors.
Input thresholds match standard LS-TTL levels (VIL ≤ 0.8 V, VIH ≥ 2.0 V), and output low-level voltage is specified at 0.5 V max under 16 mA sink current. Propagation delay is 20 ns typical (A→B or B→A) at VCC = 5 V, supporting synchronous parallel data rates up to ~25 MHz in controlled impedance environments.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal bidirectional bus transceiver with open-collector outputs |
| Logic Family | LS-TTL - ensures compatibility with legacy 74LS series logic and predictable noise margins |
| Supply Voltage | 4.75 V to 5.25 V - requires stable +5 V rail; not tolerant of wider ranges |
| Output Sink Current | 16 mA per output - supports standard 4.7 kΩ pull-up on 5 V bus for wired-OR operation |
| Propagation Delay | 20 ns typical (A→B or B→A) - enables reliable timing in 25 MHz synchronous parallel transfers |
| Operating Temperature | 0°C to 70°C - commercial-grade rating suitable for indoor industrial and computing equipment |
| Package | SOP (NS) with 20 pins - surface-mount footprint compatible with automated assembly and IPC-7351 land patterns |
Pinout & Package
SOP-20 (NS) package: 12.8 mm × 7.5 mm body, 1.27 mm pitch, 2.65 mm max height, RoHS-compliant NiPdAu lead finish, moisture sensitivity level 1 (unlimited floor life at <30°C/60% RH).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR A) | Direction control for A→B path (bits A0–A3) | High = A-to-B enabled; Low = B-to-A enabled; overrides OE_A when active |
| 2–5 (A0–A3) | Input/output port A (nibble 0) | Bidirectional data lines tied to local subsystem; open-collector outputs require external pull-up |
| 6 (GND) | Ground reference | Primary return path for all internal logic and output sinks |
| 7–10 (B0–B3) | Input/output port B (nibble 0) | Bidirectional data lines connected to shared bus; same electrical behavior as A-side |
| 11 (OE A) | Output enable for A-side (A0–A3) | Low = outputs active; High = high-impedance state - used for bus contention avoidance |
| 12 (VCC) | Positive supply | +5 V power input; decoupling capacitor required within 10 mm of pin |
| 13 (OE B) | Output enable for B-side (B0–B3) | Independent control allows selective isolation of either nibble on shared bus |
| 14–17 (B4–B7) | Input/output port B (nibble 1) | Second 4-bit segment sharing same DIR and OE controls as B0–B3 |
| 18 (DIR B) | Direction control for B→A path (bits B4–B7) | Separate DIR input enables independent direction setting for upper nibble |
| 19–20 (A4–A7) | Input/output port A (nibble 1) | Upper 4-bit segment; matches lower nibble functionality and timing |
Key Features
| Feature | Design Value |
|---|---|
| Two independent 4-bit transceivers | Enables split-bus architecture: one nibble for control/status, other for data - no external gating needed |
| Open-collector outputs | Supports wired-OR bus arbitration and mixed-voltage interfacing via external pull-up selection |
| Separate DIR and OE per nibble | Allows dynamic direction reversal and tristate control without disrupting adjacent data lanes |
| LS-TTL compatible thresholds | Guarantees interoperability with existing 74LS-based systems without level-shifting circuitry |
| SOP-20 RoHS-compliant packaging | Enables high-density PCB layouts and reflow-compatible manufacturing per J-STD-020 Level-1 |
Applications
| Industrial Backplane Interface | Legacy Parallel Printer Port |
|---|---|
Use Scenario: Interfacing microcontroller-based I/O modules to a shared 8-bit data bus in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional data bridge between local peripheral bus and system backplane; provides direction-controlled data flow and bus contention management via OE. Use Value: Eliminates need for discrete buffers and direction-control logic; open-collector outputs simplify bus termination and support multi-master arbitration. |
Use Scenario: Implementing IEEE 1284-compliant parallel port handshaking and data transfer in embedded printer controllers. IC Role / Device Role / Timing Role: Transceives STROBE, ACK, BUSY, and 8-bit data signals between host controller and printer ASIC; DIR selects data vs. status direction. Use Value: Reduces component count by integrating dual-nibble control with independent OE/DIR - critical for space-constrained printer mainboards. |
| EPROM Programming Adapter | TTL-Level Bus Extender |
Use Scenario: Adapting modern USB-to-parallel programmers to legacy EPROM burners requiring 8-bit bidirectional address/data multiplexing. IC Role / Device Role / Timing Role: Buffers and direction-controls 8-bit data/address lines between PC interface IC and EPROM socket; OE isolates bus during programming verify cycles. Use Value: Enables safe hot-plug operation and prevents bus conflicts during mode switching - essential for field-programmable memory adapters. |
Use Scenario: Extending signal reach across long PCB traces or between daughterboards in test equipment chassis. IC Role / Device Role / Timing Role: Re-drives TTL logic levels across >15 cm traces; open-collector outputs permit series-termination and reduce reflections. Use Value: Maintains signal integrity at 25 MHz without added delay-matching components - simplifies high-reliability test fixture design. |
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 | 3-state (not open-collector) outputs; single DIR control for all 8 bits; no nibble-split capability | Requires external pull-ups only if wired-OR needed; less flexible for mixed-direction nibble use | Choose when full 8-bit unidirectional control suffices and board space permits discrete pull-ups |
| SN74LS641NSR | Identical pinout and open-collector architecture; differs only in DIR logic polarity (active-low vs. SN74LS642's active-high) | Direct drop-in replacement if system firmware can invert DIR signal timing or add inverter gate | Prefer when redesigning for lower propagation skew - SN74LS641 offers 18 ns typical tPD |
Compared with SN74LS642NSR, SN74LS245N lacks nibble-level direction control and open-collector flexibility, while SN74LS641NSR delivers faster timing but requires signal polarity adaptation - both serve distinct trade-offs in legacy bus architecture upgrades.
Availability
SN74LS642NSR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy parallel port implementations, EPROM programming adapters, and TTL-level bus extender designs requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74LS642NSR 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 SN74LS642NSR belongs to TI's legacy 74LS logic family, engineered for reliability and interoperability in retrofitted industrial control systems and maintenance-critical legacy equipment interfaces.
FAQ
What is the maximum sink current per output pin on the SN74LS642NSR?
The SN74LS642NSR specifies a maximum output sink current of 16 mA per open-collector pin at VOL ≤ 0.5 V, tested under standard LS-TTL conditions (VCC = 5 V, TA = 25°C). This rating supports common 4.7 kΩ pull-up configurations on 5 V buses. Exceeding 16 mA risks exceeding absolute maximum ratings and may degrade long-term reliability.
Does the SN74LS642NSR support hot-swap or live-insertion on a powered bus?
The SN74LS642NSR does not include built-in hot-swap protection or power-on reset circuitry. While its open-collector outputs tolerate bus pre-charging, applying VCC after bus voltage may cause latch-up or excessive current through input clamps. TI recommends sequencing VCC before bus activation and using series current-limiting resistors on inputs for live-insertion scenarios involving SN74LS642NSR.
Can the SN74LS642NSR be used with 3.3 V logic systems?
The SN74LS642NSR is strictly a 5 V device: its inputs require LS-TTL thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V), and it draws supply current only from a 4.75–5.25 V rail. Direct connection to 3.3 V logic risks undriven inputs and potential damage due to input clamp conduction. Use level translators like SN74LVC4245A when interfacing SN74LS642NSR with 3.3 V systems.
What is the function of Pin 18 (DIR B) on the SN74LS642NSR?
Pin 18 (DIR B) controls data direction for the upper nibble (B4–B7 ↔ A4–A7) independently of the lower nibble. When high, data flows from port B to port A; when low, data flows from port A to port B. This separation allows simultaneous bidirectional operation - e.g., status reads on B0–B3 while writing data on A4–A7 - a capability not found in single-DIR transceivers like SN74LS245.
Is there a drop-in replacement for the SN74LS642NSR with improved ESD tolerance?
No direct drop-in replacement with enhanced ESD tolerance exists in the 74LS family. The SN74LS642NSR meets standard JEDEC JS-001 Class H2 (2 kV HBM) requirements. For higher ESD robustness, consider the SN74LVCH16245A (16-bit, 3.3 V) with ±8 kV HBM, but it requires voltage translation and layout changes. TI does not offer an LS-compatible 20-pin SOP transceiver with >2 kV HBM rating.
SN74LS642NSR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SOIC (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- 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-SO
SN74LS642NSR FAQ
1.How can I place an order for SN74LS642NSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS642NSR 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 SN74LS642NSR reliable?
The price and inventory of SN74LS642NSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS642NSR is usually 5 days.
3.What payment methods are accepted for SN74LS642NSR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS642NSR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS642NSR?
SN74LS642NSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS642NSR 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 SN74LS642NSR?
For technical support, including SN74LS642NSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS642NSR requirements.
6.How does Aetrix verify that SN74LS642NSR is sourced from the original manufacturer or authorized distributors?
All SN74LS642NSR 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 SN74LS642NSR meets industry standards.
7.What is the process for return or replacement of SN74LS642NSR?
All SN74LS642NSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS642NSR, 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 SN74LS642NSR part is unused and in its original packaging.
Return procedure for SN74LS642NSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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