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Texas Instruments SN74ALS642A-1N
- Part No.:
- SN74ALS642A-1N
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74ALS642A-1N.pdf
- Description:
- IC TRANSCEIVER INVERT 5.5V 20DIP
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
SN74ALS642A-1N from Texas Instruments is an inverting octal bus transceiver in a 20-pin PDIP package, designed for asynchronous bidirectional data transfer between A and B 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 - used in legacy industrial backplane interfaces and board-to-board communication.
For engineers reviewing the SN74ALS642A-1N datasheet, SN74ALS642A-1N pinout, SN74ALS642A-1N application, or SN74ALS642A-1N equivalent, key selection criteria include its inverting logic behavior, -1 version's enhanced 48 mA sink capability, 300-mil DIP footprint compatibility, and isolation functionality under OE high.
Technical Context
The SN74ALS642A-1N implements dual 8-bit bidirectional data paths controlled by DIR and OE inputs: DIR = L routes B→A with inversion; DIR = H routes A→B with inversion. Its ALS (Advanced Low-power Schottky) process delivers lower power than standard AS while retaining speed advantages over LS families.
It operates strictly as a 3-state transceiver - no internal latching or clocking - requiring external timing coordination. All I/O ports support 7 V absolute max input voltage, and the -1 suffix denotes increased IOL rating (48 mA vs. 24 mA in standard SN74ALS642A), valid only at VCC = 4.75–5.25 V.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Supply Voltage | 4.5 V to 5.5 V - compatible with standard 5 V TTL systems; operation outside this range invalidates specs. |
| IOL Output Current | 48 mA (−1 version only) - enables direct driving of multiple TTL loads or termination-resistor networks without buffers. |
| Propagation Delay | 10–30 ns (tPLH/tPHL) - supports synchronous bus rates up to ~15 MHz in point-to-point configurations. |
| Operating Temperature | 0°C to 70°C - rated for commercial/industrial ambient environments, not extended or automotive grade. |
| Logic Function | Inverting transceiver - data passed from A to B or B to A is inverted; critical for signal polarity planning in bus design. |
| Input Voltage Levels | VIH = 2 V, VIL = 0.8 V - fully compatible with standard TTL input thresholds and noise margins. |
| Output Voltage Levels | VOH ≥ 5.5 V (min), VOL ≤ 0.5 V (max at 48 mA) - ensures robust high/low logic discrimination under full load. |
Pinout & Package
SN74ALS642A-1N uses a 20-pin plastic dual in-line package (PDIP, 300-mil width), with 0.1-inch lead pitch and through-hole mounting. Pin 1 is located at the top-left corner (notch side left, dot marking).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Determines data flow direction: low = B→A, high = A→B; active-high logic with TTL-compatible thresholds. |
| 2 (A1) | Port A Data I/O | First bit of A-side bidirectional bus; connected to A bus when OE = L and DIR sets direction. |
| 3–9 (A2–A8) | Port A Data I/O | A-side bits 2–8; all eight A pins share identical electrical characteristics and 3-state control. |
| 10 (GND) | Ground Reference | Primary digital ground return; must be low-impedance connection to minimize noise coupling into bus lines. |
| 11–18 (B1–B8) | Port B Data I/O | B-side bidirectional data lines; electrically symmetrical to A port, supporting same drive strength and timing. |
| 19 (OE) | Output Enable Input | Active-low control: OE = L enables transceiver; OE = H places all A/B pins in high-impedance state for bus isolation. |
| 20 (VCC) | Power Supply | +5 V supply pin; requires local 0.1 µF ceramic decoupling capacitor placed within 1 cm of this pin. |
Key Features
| Feature | Design Value |
|---|---|
| Inverting bidirectional logic | Ensures signal polarity consistency across bus segments where inversion is required by system architecture or protocol layer. |
| 48 mA sink capability (−1 version) | Supports direct interface to legacy TTL loads (e.g., 74LS series) without external drivers, reducing component count on backplane cards. |
| True 3-state outputs | Provides complete electrical isolation between A and B buses when OE = H - essential for multi-master bus arbitration and hot-swap safety. |
| ALS process technology | Delivers 15 mA typical ICC (outputs high) at 5 V - ~50% lower power than equivalent AS devices while maintaining sub-30 ns propagation delays. |
| Standard 20-pin DIP footprint | Enables drop-in replacement in existing through-hole PCB designs originally using SN74ALS641A, SN74ALS642A, or SN74AS641. |
Applications
| Industrial Backplane Interface | Legacy Computer Bus Extension |
|---|---|
Use Scenario: Connecting CPU card and peripheral expansion cards via shared parallel bus in programmable logic controllers (PLCs). IC Role / Device Role / Timing Role: Bidirectional data routing element enabling read/write cycles between master and slave modules with direction switching synchronized to control strobes. Use Value: Inverting logic matches legacy bus signaling conventions; 48 mA drive ensures reliable signal integrity across 12-inch ribbon cable runs with multiple stubs. | Use Scenario: Extending ISA or Multibus I signals between motherboard and add-on I/O cards in test equipment and data acquisition systems. IC Role / Device Role / Timing Role: Isolating and translating data between two independent bus segments during DMA transfers or interrupt acknowledge cycles. Use Value: OE-controlled 3-state operation prevents bus contention during arbitration; DIP package allows manual rework and field replacement in service depots. |
| Modular Instrumentation Chassis | Repairable Embedded Controller Board |
Use Scenario: Interfacing analog front-end modules and digital processing units inside modular benchtop instruments (e.g., oscilloscopes, spectrum analyzers). IC Role / Device Role / Timing Role: Synchronizing data flow between ADC/DAC subsystems and microcontroller-based control logic using DIR-driven handshaking. Use Value: Propagation delay <30 ns ensures timing alignment with 20 MHz sampling clocks; inverting function compensates for signal inversion in analog path stages. | Use Scenario: Replacing failed transceivers on aging embedded controller boards used in factory automation HMIs and motion controllers. IC Role / Device Role / Timing Role: Restoring bidirectional communication between microcontroller and external memory or peripheral ASICs after field failure. Use Value: Identical pinout and logic behavior to original SN74ALS642A-1N allows zero-change PCB repair; RoHS-compliant NIPDAU finish meets current compliance requirements. |
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 version (non-−1); IOL = 24 mA max instead of 48 mA; otherwise identical pinout, timing, and logic. | Suitable for lighter bus loads (≤4 TTL inputs); insufficient for driving terminated lines or long traces with heavy capacitive loading. | Select SN74ALS642AN only if system-level IOL requirement is confirmed ≤24 mA and no future bus expansion is planned. |
| SN74AS641N | True (non-inverting) logic; higher speed (tPHL down to 1 ns), higher power (ICC up to 136 mA), and 64 mA IOL - but incompatible logic polarity. | Requires redesign of upstream/downstream logic to accommodate non-inverted data path; best for new high-speed designs where polarity is flexible. | Choose SN74AS641N only when replacing SN74ALS642A-1N in a new layout where inversion can be removed from firmware or external logic. |
Compared with SN74ALS642AN, the SN74ALS642A-1N provides double the output sink strength for legacy bus loading, while SN74AS641N trades polarity compatibility for raw speed - making SN74ALS642A-1N the optimal choice for drop-in repair or incremental upgrades of existing inverting-bus systems.
Availability
SN74ALS642A-1N is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy computer bus extensions, and modular instrumentation chassis requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS642A-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 ICs with broad industrial, automotive, and communications product portfolios.
The SN74ALS642A-1N belongs to TI's legacy 74ALS logic family, engineered specifically for high-reliability, medium-speed bidirectional bus interfacing in commercial and industrial systems where power efficiency and pin compatibility outweigh cutting-edge speed.
FAQ
What logic function does the SN74ALS642A-1N implement?
The SN74ALS642A-1N is an inverting octal bus transceiver: data transferred from A to B or B to A is logically inverted. This behavior is fixed and inherent to the device - not configurable. The SN74ALS642A-1N differs from the true-logic SN74ALS641A-1N solely in this inversion property, sharing identical pinout, timing, and electrical specs otherwise.
Does SN74ALS642A-1N support 3.3 V operation?
No, SN74ALS642A-1N is specified only for 4.5 V to 5.5 V VCC operation. Its input thresholds (VIH = 2 V, VIL = 0.8 V) and output drive are optimized for 5 V TTL systems. Applying 3.3 V violates recommended operating conditions and may result in undefined logic states, excessive ICC, or premature device failure.
What is the significance of the "−1" suffix in SN74ALS642A-1N?
"−1" indicates the enhanced-output version: SN74ALS642A-1N guarantees 48 mA low-level output current (IOL), versus 24 mA for the standard SN74ALS642AN. This rating applies only when VCC is maintained between 4.75 V and 5.25 V. The SN74ALS642A-1N retains identical pinout, timing, and logic function as the base part.
Can SN74ALS642A-1N replace SN74ALS641A-1N on the same PCB?
No - SN74ALS642A-1N cannot directly replace SN74ALS641A-1N because they implement opposite logic functions: SN74ALS642A-1N is inverting, while SN74ALS641A-1N is true. Swapping them would invert all data bits, causing functional failure unless compensated by upstream/downstream logic changes. Their pinouts are identical, but logic behavior is incompatible.
Is SN74ALS642A-1N RoHS compliant?
Yes, SN74ALS642A-1N is RoHS compliant per TI's packaging addendum: it features NIPDAU (nickel-palladium-gold) lead finish and meets EU Directive 2011/65/EU requirements. The "Yes" RoHS status is explicitly documented for orderable part number SN74ALS642A-1N in TI's official packaging data dated July 2026.
SN74ALS642A-1N 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-1N FAQ
1.How can I place an order for SN74ALS642A-1N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS642A-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 SN74ALS642A-1N reliable?
The price and inventory of SN74ALS642A-1N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS642A-1N is usually 5 days.
3.What payment methods are accepted for SN74ALS642A-1N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS642A-1N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS642A-1N?
SN74ALS642A-1N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS642A-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 SN74ALS642A-1N?
For technical support, including SN74ALS642A-1N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS642A-1N requirements.
6.How does Aetrix verify that SN74ALS642A-1N is sourced from the original manufacturer or authorized distributors?
All SN74ALS642A-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 SN74ALS642A-1N meets industry standards.
7.What is the process for return or replacement of SN74ALS642A-1N?
All SN74ALS642A-1N units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS642A-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 SN74ALS642A-1N part is unused and in its original packaging.
Return procedure for SN74ALS642A-1N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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