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Texas Instruments SN74ALS642A-1NE4
- Part No.:
- SN74ALS642A-1NE4
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74ALS642A-1NE4.pdf
- Description:
- BUS TRANSCEIVER, ALS SERIES, 1-F
- Quantity:
- Payment:
- Shipping:
Inventory:110
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Product details
Overview
SN74ALS642A-1NE4 from Texas Instruments is an inverting octal bus transceiver in a 20-pin plastic DIP (N) package, designed for asynchronous bidirectional data transfer between two 8-bit buses. It features direction control (DIR), output enable (OE), 48 mA low-level output drive (IOL), 0°C to 70°C operating range, and TTL-compatible logic levels. It is used in legacy industrial backplane interfaces requiring bus isolation and level translation.
For engineers reviewing the SN74ALS642A-1NE4 datasheet, SN74ALS642A-1NE4 pinout, SN74ALS642A-1NE4 application, or SN74ALS642A-1NE4 equivalent, key selection criteria include its inverting logic behavior, -1 version's enhanced 48 mA sink capability, 300-mil DIP footprint, DIR/OE dual-control architecture, and compatibility with ALS-family timing and drive specifications.
Technical Context
The SN74ALS642A-1NE4 implements a true 8-bit bidirectional transceiver with inverting logic polarity: data propagates from A-to-B when DIR = HIGH and from B-to-A when DIR = LOW. Its 3-state outputs are independently disabled by OE = HIGH, achieving high-impedance isolation between buses.
It operates strictly within 4.5 V–5.5 V VCC, supports 50 pF load capacitance, and delivers guaranteed tPHL/tPLH ≤ 38 ns (max) under worst-case conditions. The -1 suffix denotes increased IOL rating (48 mA vs. 24 mA standard), validated only at VCC = 4.75–5.25 V.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - Ensures stable operation across standard TTL supply tolerances without regulation. |
| IOL (max) | 48 mA - Supports driving heavier capacitive loads or multiple TTL inputs without external buffers. |
| tPHL/tPLH (max) | 38 ns - Enables reliable 26+ MHz bus switching in synchronous systems with margin. |
| Operating Temp | 0°C to 70°C - Qualified for commercial/industrial ambient environments, not extended temp. |
| Logic Polarity | Inverting - Output bus state is logically inverted relative to input bus during active transfer. |
| VIL/VIH | 0.8 V / 2.0 V - Matches standard TTL input thresholds for seamless integration with 74LS/ALS logic families. |
| Package | PDIP-20 (300-mil) - Through-hole mounting compatible with legacy PCB assembly and prototyping. |
Pinout & Package
SN74ALS642A-1NE4 uses a 20-pin plastic dual in-line package (PDIP, N package), 300-mil width, with standard DIP pin spacing (0.1 inch). Pin 1 is located at the top-left corner marked by a notch or dot.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Determines data flow direction: HIGH = A→B, LOW = B→A; TTL-compatible threshold. |
| 2 (A1) | Input/Output Port A Bit 1 | Bidirectional I/O terminal for Bus A; high-impedance when OE = HIGH or DIR conflicts. |
| 3–9 (A2–A8) | Input/Output Port A Bits 2–8 | Octal complement of A1; all share same DIR/OE control and electrical characteristics. |
| 10 (GND) | Ground Reference | Primary signal and power return path; must be low-inductance connection for noise immunity. |
| 11–18 (B1–B8) | Input/Output Port B Bits 1–8 | Octal bidirectional port for Bus B; electrically mirrored to A-side with inverting logic behavior. |
| 19 (VCC) | Positive Supply | 5 V nominal supply; decoupling capacitor required within 1 cm for transient current handling. |
| 20 (OE) | Output Enable Input | Active-LOW control: LOW enables transceiver, HIGH forces all A/B pins to high-impedance state. |
Key Features
| Feature | Design Value |
|---|---|
| Inverting Data Path | Ensures signal inversion across bus transfer-required in systems where polarity correction is embedded in protocol layer. |
| 48 mA Sink Capability (-1 version) | Enables direct drive of up to 12 standard TTL loads or termination-resistor networks without fanout buffers. |
| Dual Independent Controls (DIR + OE) | Allows precise sequencing: OE isolates buses first, then DIR selects direction-critical for glitch-free bus handoff. |
| TTL-Compatible Thresholds | Eliminates need for level-shifting circuitry when interfacing with 74LS, 74ALS, and legacy microprocessor buses. |
| 20-Pin PDIP Footprint | Supports manual soldering, socket-based testing, and drop-in replacement in existing 300-mil DIP layouts. |
Applications
| Industrial Backplane Interface | Legacy Microprocessor Bus Extension |
|---|---|
Use Scenario: Connecting isolated CPU and peripheral modules across a 200 mm backplane with stub lengths up to 50 mm. IC Role / Device Role / Timing Role: Bidirectional bus repeater that regenerates and inverts signals between two 8-bit data segments while maintaining timing integrity. Use Value: Provides 48 mA drive to overcome backplane capacitance-induced rise/fall time degradation and ensures clean edge transitions at 10–20 MHz. | Use Scenario: Extending Z80 or 8085 address/data bus to off-board memory cards in test equipment rack systems. IC Role / Device Role / Timing Role: Direction-controlled transceiver enabling CPU-initiated reads/writes to external RAM/ROM banks via shared bus lines. Use Value: Inverting logic matches native bus polarity requirements of certain memory controllers; OE gating prevents bus contention during DMA cycles. |
| Programmable Logic Interfacing | Test Equipment Signal Routing |
Use Scenario: Interfacing FPGA I/O banks (3.3 V LVTTL) to legacy 5 V TTL subsystems using level-shifting resistors and bus transceivers. IC Role / Device Role / Timing Role: Voltage-tolerant bidirectional buffer that translates and inverts logic states between domains under DIR-synchronized control. Use Value: Eliminates need for discrete inverters; 38 ns max propagation delay allows synchronization with 25 MHz FPGA clock domains. | Use Scenario: Automated test fixture routing signals between DUT connector and instrument I/O ports using programmable bus switches. IC Role / Device Role / Timing Role: Reconfigurable bus gate controlled by test sequencer to isolate or connect signal paths on demand. Use Value: OE-driven high-impedance state guarantees no leakage or loading during path reconfiguration; DIR enables loopback diagnostics. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar bidirectional bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS642AN | Standard (non–-1) version with 24 mA IOL; identical pinout, timing, and logic function. | Suitable for lighter loads (<8 TTL units); lower power consumption in quiescent state. | Select when drive strength >24 mA is unnecessary and cost optimization is prioritized. |
| SN74AS641N | True (non-inverting) logic; higher speed (7.5 ns tPHL max); 64 mA IOL; AS family propagation characteristics. | Used where signal polarity preservation is mandatory and faster settling is required. | Choose only if system design requires non-inverted data path and can accommodate AS-family higher ICC and tighter layout constraints. |
Compared with SN74ALS642AN, SN74ALS642A-1NE4 provides double the sink current for robust bus driving; compared with SN74AS641N, it trades speed and non-inverting behavior for ALS-family power efficiency and established thermal stability in dense board layouts.
Availability
SN74ALS642A-1NE4 is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy microprocessor bus extensions, programmable logic interfacing, and test equipment signal routing requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS642A-1NE4 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 with over 90 years of analog and logic IC innovation, headquartered in Dallas, Texas.
The SN74ALS642A-1NE4 belongs to TI's legacy 74ALS logic family, engineered for high-speed, low-power bidirectional bus communication in industrial control, instrumentation, and computing systems where reliability and pin compatibility across generations are critical.
FAQ
What logic polarity does the SN74ALS642A-1NE4 implement?
The SN74ALS642A-1NE4 implements inverting logic: data transferred from A to B or B to A is logically inverted at the output. This is intrinsic to the device's architecture and cannot be disabled. The SN74ALS642A-1NE4 datasheet confirms this behavior in the function table and logic diagrams, distinguishing it from the true-logic SN74ALS641A series.
What is the maximum output sink current supported by the SN74ALS642A-1NE4?
The SN74ALS642A-1NE4 supports a maximum low-level output current (IOL) of 48 mA per pin, but only when VCC is maintained between 4.75 V and 5.25 V. This enhanced drive is the defining feature of the "-1" suffix variant and is explicitly specified in the recommended operating conditions table of the SN74ALS642A-1NE4 datasheet.
Can the SN74ALS642A-1NE4 be used interchangeably with SN74ALS642AN?
The SN74ALS642A-1NE4 and SN74ALS642AN share identical pinout, logic function, timing, and package, making them physically and electrically interchangeable. However, the SN74ALS642A-1NE4 provides 48 mA IOL versus 24 mA for the standard version-so substitution is safe only if the higher drive is not required or may cause excessive loading.
What is the operating temperature range for the SN74ALS642A-1NE4?
The SN74ALS642A-1NE4 is characterized for operation from 0°C to 70°C ambient temperature, as confirmed in the recommended operating conditions table. It is not rated for extended industrial (–40°C to 85°C) or automotive temperature ranges, and performance outside this window is not guaranteed.
Does the SN74ALS642A-1NE4 require external pull-up resistors on its I/O pins?
No, the SN74ALS642A-1NE4 does not require external pull-up resistors on A or B port pins during active operation, as its totem-pole outputs actively drive both logic HIGH and LOW states. Pull-ups may be needed only in high-impedance (OE = HIGH) states for defined idle levels-but system design must verify bus topology and termination requirements separately.
SN74ALS642A-1NE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- 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:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74ALS642A-1NE4 FAQ
1.How can I place an order for SN74ALS642A-1NE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS642A-1NE4 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 SN74ALS642A-1NE4 reliable?
The price and inventory of SN74ALS642A-1NE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS642A-1NE4 is usually 5 days.
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SN74ALS642A-1NE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS642A-1NE4 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 SN74ALS642A-1NE4?
For technical support, including SN74ALS642A-1NE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS642A-1NE4 requirements.
6.How does Aetrix verify that SN74ALS642A-1NE4 is sourced from the original manufacturer or authorized distributors?
All SN74ALS642A-1NE4 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 SN74ALS642A-1NE4 meets industry standards.
7.What is the process for return or replacement of SN74ALS642A-1NE4?
All SN74ALS642A-1NE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS642A-1NE4, 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 SN74ALS642A-1NE4 part is unused and in its original packaging.
Return procedure for SN74ALS642A-1NE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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