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Texas Instruments SN74LS642N
- Part No.:
- SN74LS642N
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS642N.pdf
- Description:
- IC TXRX INVERT 5.25V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:4,325
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Product details
Overview
SN74LS642N 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 independent enable controls for A-to-B and B-to-A directions, 35 mA sink capability per output, and operates across 0°C to 70°C. It is used in legacy industrial backplane interfaces and microprocessor system address/data bus isolation.
For engineers reviewing the SN74LS642N datasheet, SN74LS642N pinout, SN74LS642N application, or SN74LS642N equivalent, key selection criteria include open-collector drive strength, direction-control timing compatibility with LS-TTL logic families, thermal derating at elevated ambient temperatures, and PDIP-20 mechanical fit in through-hole board layouts.
Technical Context
The SN74LS642N implements dual 8-bit bidirectional bus transceivers with separate active-low A-enable (1G, 2G) and B-enable (1G̅, 2G̅) inputs, enabling independent control of data flow in each direction. 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 typical propagation delay of 20 ns (max), input threshold compatible with standard TTL, and guaranteed DC output voltage levels down to 0.5 V at 35 mA sink load. No internal clamping diodes are present - external transient protection must be added in noisy environments.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS (Low-power Schottky TTL) - ensures compatibility with legacy LS-TTL systems and predictable noise margins. |
| Function | Octal bidirectional bus transceiver with open-collector outputs - enables shared bus arbitration and wired-OR signaling. |
| Output Sink Current | 35 mA per output - supports driving multiple TTL inputs or moderate-current LEDs without external buffers. |
| Propagation Delay | 20 ns max (A-to-B or B-to-A) - meets timing budgets in 8 MHz–12 MHz synchronous bus designs. |
| Operating Temperature | 0°C to +70°C - validated for commercial-grade embedded control and instrumentation applications. |
| Supply Voltage | VCC = 4.75 V to 5.25 V - requires stable 5 V rail; no internal regulation or brown-out detection. |
| Package | PDIP-20 (0.300" wide) - through-hole mounting with 2.54 mm pitch; compatible with standard DIP sockets and wave-solder processes. |
Pinout & Package
SN74LS642N uses a 20-pin plastic dual in-line package (PDIP-N) with 0.300" body width and 2.54 mm lead pitch. Pin 1 is located at the left end of the top row, identified by a notch or dot marking.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (1G) | A-to-B direction enable (active low) | When low, enables data transfer from A-bus to B-bus; high disables A→B path and places B outputs in high-impedance state. |
| 2–9 (A1–A8) | Input/Output port A | Bidirectional I/O pins for first 8-bit bus; driven by external source when enabled as output, or read as inputs when not driven. |
| 10 (GND) | Ground reference | Primary signal and power return; must be low-inductance connection to minimize ground bounce in high-speed switching. |
| 11–18 (B1–B8) | Input/Output port B | Bidirectional I/O pins for second 8-bit bus; functionally identical to A1–A8 but electrically isolated when both enables are inactive. |
| 19 (2G) | B-to-A direction enable (active low) | When low, enables data transfer from B-bus to A-bus; high disables B→A path and places A outputs in high-impedance state. |
| 20 (VCC) | Positive supply | 5 V ±5% DC supply; decoupling capacitor (0.1 µF ceramic) required within 1 cm of this pin for stable operation. |
Key Features
| Feature | Design Value |
|---|---|
| Open-collector outputs | Enable wired-AND bus sharing, level translation up to 15 V, and direct interface to electromechanical relays or optocouplers. |
| Independent directional control | Separate 1G and 2G enables allow asymmetric bus arbitration - e.g., A→B active while B→A is disabled for unidirectional write-only transfers. |
| High sink current (35 mA) | Drives up to 10 standard TTL loads per output without external buffering, reducing component count in legacy backplane designs. |
| LS-TTL compatible thresholds | VIL ≤ 0.8 V and VIH ≥ 2.0 V ensure reliable interfacing with 74LS, 74S, and 74F logic families without level-shifting circuitry. |
| Commercial temperature range | 0°C to +70°C operation verified across full VCC range - suitable for non-military industrial controllers and test equipment. |
Applications
| Industrial Backplane Interface | Microprocessor Address Bus Isolation |
|---|---|
Use Scenario: Interfacing multiple 8-bit peripheral cards to a shared backplane in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional data transceiver managing read/write cycles between CPU and I/O modules via open-collector arbitration lines. Use Value: Enables hot-swappable card insertion without bus contention; 35 mA sink handles termination resistors and multiple TTL loads on same line. |
Use Scenario: Isolating Z80 or 8085 CPU address bus from memory-mapped peripherals during DMA operations. IC Role / Device Role / Timing Role: Direction-controlled buffer preventing address bus corruption when peripherals drive addresses during bus grant cycles. Use Value: Independent 1G/2G enables allow precise timing alignment with HOLD/HOLDA signals, eliminating address glitches during bus handoff. |
| Legacy Test Equipment Bus Expansion | Parallel Printer Port Logic Level Translation |
Use Scenario: Extending GPIB-compatible parallel control bus in automated test systems using discrete TTL logic. IC Role / Device Role / Timing Role: Octal transceiver translating between controller-side LS-TTL levels and instrument-side 12 V logic rails via pull-up resistors. Use Value: Open-collector outputs simplify level translation without dedicated level shifters; 20 ns delay preserves setup/hold timing in 1–2 MHz control sequences. |
Use Scenario: Adapting Centronics-style printer port signals to drive external LED status indicators or relay-based paper feed controls. IC Role / Device Role / Timing Role: Output driver converting 5 V TTL logic to 12 V/24 V switched loads using external pull-ups and flyback diodes. Use Value: 35 mA per output directly drives common 12 V LEDs or small solenoids; no additional transistor stage required for low-duty-cycle indicators. |
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; no built-in wired-AND capability; 24 mA sink only. | Requires external pull-ups for wired-logic; unsuitable for direct level translation above 5 V. | Select when bus isolation without shared-line arbitration is sufficient and lower power consumption is prioritized. |
| SN74LS641N | Same open-collector architecture and pinout; differs only in enable polarity (active-high vs. SN74LS642N's active-low). | Requires inverted control logic; may necessitate gate-level inversion in existing enable signal paths. | Select when system control logic naturally provides high-active enables and PCB layout reuse is critical. |
Compared with SN74LS245N, SN74LS642N provides superior bus-sharing flexibility via open-collector outputs, while SN74LS641N offers identical electrical behavior with inverted enable polarity - making it a drop-in replacement only if enable signal inversion is accommodated in firmware or glue logic.
Availability
SN74LS642N is available at Aetrix Electronics and suitable for industrial backplane interfaces, microprocessor bus isolation, and legacy test equipment requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS642N 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 solutions with broad industrial and automotive qualification.
The SN74LS642N belongs to TI's legacy 74LS logic portfolio, engineered for reliability in fixed-function digital systems where deterministic timing, noise immunity, and long-lifecycle support are essential.
FAQ
What is the maximum sink current per output of the SN74LS642N?
The SN74LS642N guarantees a minimum output sink current of 35 mA per pin under VCC = 5 V and TA = 25°C conditions, as specified in the SDLS189 datasheet. This rating holds across the full 0°C to +70°C operating range with appropriate thermal derating above 50°C ambient. The SN74LS642N maintains consistent performance without requiring external current-limiting resistors for standard TTL fanout.
Does the SN74LS642N support bidirectional data flow on the same pins?
Yes, the SN74LS642N supports true bidirectional operation: pins A1–A8 and B1–B8 serve as shared I/O ports whose direction is controlled by the 1G and 2G enable inputs. When 1G is low and 2G is high, data flows A→B; when 2G is low and 1G is high, data flows B→A. Both enables high places all outputs in high-impedance state - a feature confirmed in the functional description of the SN74LS642N datasheet.
Can the SN74LS642N be used with 3.3 V logic systems?
No, the SN74LS642N is strictly a 5 V TTL device with VCC specification of 4.75 V to 5.25 V and input thresholds aligned to standard TTL levels (VIL ≤ 0.8 V, VIH ≥ 2.0 V). It lacks 3.3 V tolerance and will not reliably interface with 3.3 V CMOS or LVTTL without level-shifting circuitry. The SN74LS642N is incompatible with mixed-voltage systems unless external translators are employed.
What is the propagation delay of the SN74LS642N?
The SN74LS642N has a maximum propagation delay of 20 ns (typical 15 ns) for both A-to-B and B-to-A signal paths, measured under standard test conditions (VCC = 5 V, CL = 15 pF, TA = 25°C). This value is explicitly listed in the "Switching Characteristics" table of the SDLS189 datasheet and remains valid across the full commercial temperature range when operated within rated VCC limits.
Is the SN74LS642N pin-compatible with other devices in the SN74LS64x family?
Yes, the SN74LS642N shares identical pinout and package (PDIP-20) with SN74LS641N and SN74LS644N, as confirmed by the "PIN CONFIGURATIONS" diagram in the SDLS189 datasheet. However, functional differences exist: SN74LS641N uses active-high enables, while SN74LS644N integrates 3-state (not open-collector) outputs. Physical compatibility does not imply electrical or functional interchangeability without design validation.
SN74LS642N 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:
- -, 24mA
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74LS642N FAQ
1.How can I place an order for SN74LS642N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS642N 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 SN74LS642N reliable?
The price and inventory of SN74LS642N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS642N is usually 5 days.
3.What payment methods are accepted for SN74LS642N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS642N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS642N?
SN74LS642N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS642N 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 SN74LS642N?
For technical support, including SN74LS642N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS642N requirements.
6.How does Aetrix verify that SN74LS642N is sourced from the original manufacturer or authorized distributors?
All SN74LS642N 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 SN74LS642N meets industry standards.
7.What is the process for return or replacement of SN74LS642N?
All SN74LS642N units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS642N, 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 SN74LS642N part is unused and in its original packaging.
Return procedure for SN74LS642N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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