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Texas Instruments SN74ALS642AN
- Part No.:
- SN74ALS642AN
- Manufacturer:
- Texas Instruments
- Package:
- -
- Datasheet:
-
SN74ALS642AN.pdf
- Description:
- BUS TRANSCEIVER, ALS SERIES
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Inventory:2,030
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Product details
Overview
SN74ALS642AN from Texas Instruments is an inverting octal bus transceiver in a 20-pin plastic DIP (N) package, designed for asynchronous bidirectional data transfer between A and B buses. It features direction control (DIR), output enable (OE), 24 mA low-level output drive, 0.5 V max VOL at IOL = 24 mA, and operates from 0°C to 70°C.
For engineers reviewing the SN74ALS642AN datasheet, SN74ALS642AN pinout, SN74ALS642AN application, or SN74ALS642AN equivalent, this page delivers verified electrical specs, true inverting logic behavior, isolation timing, bus-isolation use cases, and direct alternatives with documented functional alignment.
Technical Context
The SN74ALS642AN implements TTL-compatible inverting transceiver logic: when DIR = L, data flows from B bus to A bus with inversion; when DIR = H, data flows from A bus to B bus with inversion. OE = H forces all outputs into high-impedance state regardless of DIR.
It uses bipolar ALS (Advanced Low-Power Schottky) technology, delivering 24 mA sink current capability, 0.4 V typical VOL at 24 mA, and propagation delays as low as 5 ns (tPLH) under 50 pF load - optimized for legacy parallel bus systems requiring deterministic signal polarity and bus contention avoidance.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V TTL logic rails without regulation overhead |
| Logic Type | Inverting - each data path (A↔B) flips signal polarity during transmission, critical for differential bus signaling or level-shifted interface matching |
| IOL (max) | 24 mA - sufficient to drive multiple TTL loads (fan-out ≥10) without external buffers |
| VOL (max) | 0.5 V at IOL = 24 mA - ensures robust low-state noise margin in noisy industrial backplanes |
| tPHL/tPLH | 3–30 ns - supports 33 MHz burst-mode bus operation with 50 pF load and 680 Ω termination |
| Operating Temp | 0°C to 70°C - qualified for commercial-grade embedded control and instrumentation applications |
| Input Thresholds | VIH = 2.0 V, VIL = 0.8 V - matches standard TTL input compatibility, eliminating level-shifter requirements |
Pinout & Package
SN74ALS642AN is housed in a 20-pin plastic dual in-line package (PDIP-N), 300-mil width, 0.100" lead pitch, with standard through-hole mounting and JEDEC MS-001 compliant footprint.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Determines data flow direction: DIR = L enables B→A (inverted), DIR = H enables A→B (inverted) |
| 2 (A1) | Port A Data I/O | First bit of A-side bidirectional bus; inverted relative to corresponding B port during active transfer |
| 3–9 (A2–A8) | Port A Data I/O | Octal A-bus inputs/outputs; all eight bits invert simultaneously per DIR setting |
| 10 (GND) | Ground Reference | Primary power return for logic core and I/O drivers; must be low-impedance for noise immunity |
| 11–18 (B1–B8) | Port B Data I/O | Octal B-bus inputs/outputs; inverted relative to corresponding A port during active transfer |
| 19 (VCC) | Supply Voltage | +5 V power rail; decoupling capacitor required within 1 cm for stable switching performance |
| 20 (OE) | Output Enable Input | Active-low control: OE = L enables transceiver function; OE = H places all A/B pins in high-Z state for bus isolation |
Key Features
| Feature | Design Value |
|---|---|
| Inverting Transceiver Logic | Guarantees signal polarity inversion across both A→B and B→A paths, enabling direct integration with complementary bus architectures |
| High-Current Sink Outputs | 24 mA IOL rating allows direct driving of multiple TTL inputs or LED indicators without external drivers |
| Three-State Bus Isolation | OE-controlled high-impedance mode prevents bus contention during multi-master arbitration or standby states |
| TTL-Compatible Thresholds | VIH = 2.0 V / VIL = 0.8 V eliminates need for level translation when interfacing with legacy 5 V microcontrollers and peripherals |
| ALS Process Technology | Combines Schottky clamping with low-power design for 15 mA typical ICC (outputs high), reducing thermal load in dense PCB layouts |
Applications
| Industrial Backplane Interface | Legacy Microcontroller Expansion Bus |
|---|---|
Use Scenario: Connecting isolated PLC I/O modules to a central controller via shared 8-bit parallel backplane. IC Role / Device Role / Timing Role: Bidirectional inverting transceiver managing data flow between master and slave cards while preventing bus conflicts during hot-swap events. Use Value: OE-controlled isolation ensures zero bus contention during module insertion/removal; inverting logic matches differential receiver inputs on downstream ADC/DAC cards. | Use Scenario: Expanding Z80 or 8085-based system memory or peripheral address/data buses using discrete glue logic. IC Role / Device Role / Timing Role: Octal inverting transceiver providing controlled A→B or B→A data routing under CPU-generated DIR/OE signals. Use Value: 5 ns minimum tPLH enables reliable 33 MHz burst transfers; 24 mA drive sustains signal integrity across 15 cm ribbon cable runs. |
| Test Equipment Digital I/O Subsystem | Automated Test Fixture Data Mux |
Use Scenario: Routing stimulus/response signals between DUT interface connectors and pattern generator/analyzer ports in benchtop ATE. IC Role / Device Role / Timing Role: Inverting bus switch enabling reversible signal path selection (DUT→analyzer or analyzer→DUT) with precise timing control. Use Value: Matched tPHL/tPLH (≤22 ns) ensures sub-50 ns round-trip latency; high-Z isolation prevents loading of sensitive analog measurement circuits. | Use Scenario: Multiplexing 8-bit sensor data streams from multiple test stations onto a single host controller bus. IC Role / Device Role / Timing Role: Direction-controlled transceiver acting as programmable data router under FPGA or CPLD supervision. Use Value: DIR-selectable flow direction eliminates need for separate transmit/receive ICs; OE gating enables time-division multiplexing without external logic. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal inverting transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS642A-1N | Same pinout and logic, but rated for 48 mA IOL (at VCC = 4.75–5.25 V); higher drive capability requires tighter VCC regulation | Preferred where driving long traces or >10 TTL loads; not drop-in if existing design relies on 24 mA thermal limits | Select SN74ALS642A-1N only when increased sink current is required and VCC stability is guaranteed. |
| SN74AS641N | True (non-inverting) logic, 64 mA IOL, faster propagation (1–7.5 ns), higher ICC (50–136 mA); different function table and voltage thresholds | Suitable for high-speed non-inverting bus extension, but incompatible for polarity-sensitive interfaces requiring inversion | Choose SN74AS641N only when inversion is unnecessary and speed/power trade-off favors AS-series performance. |
Compared with SN74ALS642AN, SN74ALS642A-1N offers higher drive strength at regulated 5 V but no logic change, while SN74AS641N provides superior speed and drive but abandons inversion - making it unsuitable for applications dependent on signal polarity reversal.
Availability
SN74ALS642AN is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy microcontroller expansion buses, test equipment digital I/O subsystems, and automated test fixture data mux applications requiring stable component supply over extended production lifecycles.
Supply support for SN74ALS642AN 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 for industrial, automotive, and communications markets.
The SN74ALS642AN belongs to TI's legacy 74ALS logic family, engineered for reliable 5 V TTL interoperability in cost-sensitive, noise-tolerant parallel bus systems deployed in industrial control and instrumentation.
FAQ
What is the logic function of SN74ALS642AN?
The SN74ALS642AN is an inverting octal bus transceiver: data transmitted from A to B or B to A is logically inverted. When DIR = L, B-bus data appears inverted on A-bus; when DIR = H, A-bus data appears inverted on B-bus. This behavior is fixed and cannot be configured as true logic.
Does SN74ALS642AN support 3.3 V operation?
No, SN74ALS642AN is specified only for 4.5 V to 5.5 V VCC operation. Its TTL-compatible input thresholds (VIH = 2.0 V, VIL = 0.8 V) and ALS process require 5 V nominal supply. Operating below 4.5 V may cause undefined logic states or excessive VOL, and is outside the recommended conditions for SN74ALS642AN.
What is the maximum capacitive load SN74ALS642AN can drive reliably?
SN74ALS642AN is characterized for CL = 50 pF in switching specifications, with tPLH/tPHL up to 30 ns. Driving loads beyond 50 pF increases propagation delay nonlinearly and may exceed setup/hold timing margins. For >50 pF traces or fanout >10, add series termination or buffer stages - the SN74ALS642AN itself does not guarantee performance beyond its tested 50 pF condition.
Can SN74ALS642AN replace SN74ALS641AN in a design?
No - SN74ALS641AN is a true (non-inverting) transceiver, while SN74ALS642AN is inverting. Swapping them without logic inversion elsewhere in the signal path will reverse all data bits, causing communication failure. The pinouts and timing are identical, but functional incompatibility makes direct replacement invalid for SN74ALS642AN.
Is SN74ALS642AN RoHS compliant?
Yes, SN74ALS642AN is RoHS compliant with NIPDAU lead finish, as confirmed in TI's Package Option Addendum. It meets EU Directive 2011/65/EU requirements and carries "Yes" in the RoHS column for all active PDIP (N) variants including SN74ALS642AN and SN74ALS642A-1N.
SN74ALS642AN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- -
- Number of Elements:
- -
- Number of Bits per Element:
- -
- Input Type:
- -
- Output Type:
- -
- Current - Output High, Low:
- -
- Voltage - Supply:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- -
- Supplier Device Package:
- -
SN74ALS642AN FAQ
1.How can I place an order for SN74ALS642AN through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS642AN 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 SN74ALS642AN reliable?
The price and inventory of SN74ALS642AN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS642AN is usually 5 days.
3.What payment methods are accepted for SN74ALS642AN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS642AN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS642AN?
SN74ALS642AN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS642AN 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 SN74ALS642AN?
For technical support, including SN74ALS642AN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS642AN requirements.
6.How does Aetrix verify that SN74ALS642AN is sourced from the original manufacturer or authorized distributors?
All SN74ALS642AN 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 SN74ALS642AN meets industry standards.
7.What is the process for return or replacement of SN74ALS642AN?
All SN74ALS642AN units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS642AN, 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 SN74ALS642AN part is unused and in its original packaging.
Return procedure for SN74ALS642AN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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