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Texas Instruments SN74ALS642A-IN
- Part No.:
- SN74ALS642A-IN
- Manufacturer:
- Texas Instruments
- Package:
- -
- Datasheet:
-
SN74ALS642A-IN.pdf
- Description:
- BUS TRANSCEIVER, ALS SERIES, 1-F
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Inventory:3,440
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Product details
Overview
SN74ALS642A-IN from Texas Instruments is an inverting octal bus transceiver IC designed for asynchronous bidirectional data transfer between two 8-bit buses (A and B) in TTL-compatible systems. It features direction control (DIR), output enable (OE), 5-V supply operation, 0°C to 70°C temperature range, and supports up to 24 mA low-level output current. It is used in legacy industrial backplane interfaces and board-to-board communication where signal inversion is required.
For engineers reviewing the SN74ALS642A-IN datasheet, SN74ALS642A-IN pinout, SN74ALS642A-IN application, or SN74ALS642A-IN equivalent, key selection criteria include its inverting logic behavior, 3-state bidirectional I/O capability, 20-pin PDIP package, guaranteed 24-mA sink drive at VCC = 4.5 V, and compatibility with ALS-family timing and voltage thresholds.
Technical Context
The SN74ALS642A-IN implements a dual-rail 3-state bus transceiver architecture with separate DIR and OE controls. Its inverting logic path ensures A→B and B→A data transmission flips bit polarity, distinguishing it from the true-logic SN74ALS641A. All I/O ports are TTL-compatible with VIH = 2 V and VIL = 0.8 V.
Propagation delays range from 5 ns (min) to 30 ns (max) across A↔B paths under CL = 50 pF and RL = 680 Ω conditions. Power consumption is optimized for ALS technology: ICC = 8–15 mA (outputs high) and 18–28 mA (outputs low) at VCC = 5.5 V, enabling lower static power than AS-series alternatives.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Type | Inverting bidirectional transceiver - outputs invert input bits during A→B or B→A transfer. |
| Supply Voltage | 4.5 V to 5.5 V - operates reliably across standard TTL 5-V rail tolerances. |
| Output Drive | 24 mA sink (IOL) at VCC = 4.5 V - sufficient to drive multiple TTL loads without external buffers. |
| Propagation Delay | 5–30 ns (tPLH/tPHL) - enables reliable operation up to ~33 MHz bus toggle rates in point-to-point configurations. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded and industrial control applications. |
| Input Thresholds | VIH = 2 V, VIL = 0.8 V - matches standard TTL logic levels for seamless integration with 74LS/ALS logic families. |
| Quiescent Current | ICC = 8–15 mA (high outputs), 18–28 mA (low outputs) at VCC = 5.5 V - lower than AS-series counterparts for reduced system power. |
Pinout & Package
SN74ALS642A-IN is supplied in a 20-pin plastic DIP (N) package, 300-mil width, with 0.1-inch lead pitch and through-hole mounting. Pin 1 is marked by a notch or beveled corner on the package top edge.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Low = B→A transfer; High = A→B transfer - determines data flow direction synchronously. |
| 2 (A1) | Bus A I/O Port | Octal A-side bidirectional data line - connects to local system bus; inverted on output to B side. |
| 3–9 (A2–A8) | Bus A I/O Ports | Remaining 7 bits of A-bus interface - all share same DIR and OE control logic. |
| 10 (GND) | Ground Reference | Power return path for logic and I/O circuits - must be low-impedance for noise immunity. |
| 11–18 (B1–B8) | Bus B I/O Ports | Octal B-side bidirectional data lines - receive inverted data from A side when DIR active. |
| 19 (OE) | Output Enable Input | Low = enabled; High = 3-state isolation - disables both A and B ports simultaneously for bus sharing. |
| 20 (VCC) | Supply Voltage | +5 V power rail - decoupling capacitor (0.1 µF) required near pin for stable switching performance. |
Key Features
| Feature | Design Value |
|---|---|
| Inverting Data Path | Guarantees bit-wise inversion during A↔B transfer - eliminates need for external inverters in differential or complemented bus schemes. |
| 3-State Bidirectional I/O | Full bus isolation when OE = high - allows multiple transceivers to share common B-bus without contention. |
| TTL-Compatible Thresholds | VIH = 2 V / VIL = 0.8 V - ensures interoperability with legacy 74LS, 74ALS, and microcontroller GPIOs. |
| ALS Technology | Lower ICC vs AS-series (e.g., SN74AS641) - reduces heat generation and supply loading in dense backplane designs. |
| 20-Pin DIP Package | Standard through-hole footprint - supports prototyping, repair, and legacy PCB rework without SMT infrastructure. |
Applications
| Industrial Backplane Interface | Legacy Microprocessor Bus Extension |
|---|---|
Use Scenario: Connecting isolated I/O modules to a central PLC CPU via parallel backplane wiring. IC Role / Device Role / Timing Role: Bidirectional level-shifting and bus isolation transceiver with inverting logic for parity or handshake signaling. Use Value: Enables deterministic A↔B data exchange with built-in 3-state control, eliminating external bus switches and reducing component count. | Use Scenario: Extending Z80 or 8085 address/data bus to peripheral cards in vintage computer or test equipment chassis. IC Role / Device Role / Timing Role: Inverting octal transceiver managing multiplexed AD bus direction and isolation during memory or I/O cycles. Use Value: Matches ALS timing specs and TTL voltage levels, ensuring setup/hold compliance with original CPU timing diagrams. |
| Test Equipment Signal Routing | Embedded Controller Subsystem Bridge |
Use Scenario: Reconfigurable signal path in automated test fixtures routing DUT signals between stimulus and measurement resources. IC Role / Device Role / Timing Role: Direction-controlled bidirectional data conduit with fast enable/disable for dynamic bus partitioning. Use Value: 30 ns max propagation delay and 3-state isolation support sub-33 MHz test pattern rates while preventing bus conflicts. | Use Scenario: Interfacing an ARM-based main controller to an FPGA-configured subsystem using parallel status/control registers. IC Role / Device Role / Timing Role: Inverting bus bridge isolating domains and adapting logic polarity between heterogeneous controllers. Use Value: Eliminates need for discrete inverters per line, simplifying layout and improving signal integrity on long parallel traces. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS641A-IN | True (non-inverting) logic path; identical pinout, timing, and electrical specs otherwise. | Used where bit-level inversion is not required - e.g., direct bus mirroring without polarity change. | Select SN74ALS641A-IN only if system logic requires non-inverted data transfer; no PCB changes needed. |
| SN74AS641-IN | Faster propagation (1–22 ns vs 5–30 ns); higher IOL (64 mA); higher ICC (50–136 mA); AS-family speed-power trade-off. | Suitable for high-speed backplanes (>25 MHz) where ALS timing margins are insufficient. | Choose SN74AS641-IN when speed outweighs power and thermal constraints; verify layout for faster edge rates. |
Compared with SN74ALS642A-IN, SN74ALS641A-IN provides identical form-factor and drive strength but lacks inversion - ideal for straightforward bus extension. SN74AS641-IN delivers significantly faster switching at the cost of doubled power draw and stricter layout requirements for signal integrity.
Availability
SN74ALS642A-IN is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy microprocessor bus extensions, and test equipment signal routing requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS642A-IN 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 SN74ALS642A-IN belongs to TI's legacy 74ALS logic family, engineered for robustness, predictable timing, and compatibility with earlier TTL systems in commercial-temperature industrial control environments.
FAQ
What is the logic function of the SN74ALS642A-IN?
The SN74ALS642A-IN is an inverting octal bus transceiver: data transferred from A to B or B to A is logically inverted bit-for-bit. This distinguishes it from the true-logic SN74ALS641A. The inversion occurs regardless of direction; DIR and OE jointly control data flow and 3-state output enablement. Its function is fully defined in the device's truth table and confirmed across all operating conditions in the SDAS300 datasheet.
Does the SN74ALS642A-IN support 3.3-V operation?
No, the SN74ALS642A-IN is specified only for 4.5 V to 5.5 V supply operation and is not rated for 3.3-V use. Its input thresholds (VIH = 2 V, VIL = 0.8 V) and output drive characteristics assume a 5-V rail. Applying 3.3 V may result in marginal or non-functional behavior, including failure to meet VOL/VOL specs or incorrect logic interpretation. For 3.3-V systems, consider modern level-shifting transceivers instead of SN74ALS642A-IN.
What package types are available for the SN74ALS642A-IN?
The SN74ALS642A-IN is offered in the standard plastic DIP (N) package - a 20-pin, 300-mil wide, through-hole format with 0.1-inch lead spacing. While other variants like SN74ALS642A-1DW exist in SOIC (DW) and SOP (NS) packages, the "-IN" suffix specifically denotes the PDIP (N) variant. Package dimensions, land patterns, and tape-and-reel details are documented in TI's DW0020A outline and packaging addendum.
How does the SN74ALS642A-IN handle bus contention?
The SN74ALS642A-IN prevents bus contention via its 3-state outputs controlled by the OE pin. When OE is high, all A and B I/O pins enter high-impedance state, electrically disconnecting both buses. This allows multiple SN74ALS642A-IN devices to share a common B-bus without conflict, provided only one has OE low at any time. DIR alone does not isolate - OE must be asserted to achieve true bus isolation.
Is there a -1 version of the SN74ALS642A-IN with higher drive capability?
Yes, the SN74ALS642A-1N is the enhanced-drive variant of the SN74ALS642A-IN, supporting up to 48 mA low-level output current (IOL) when VCC is between 4.75 V and 5.25 V. The standard SN74ALS642A-IN is rated for 24 mA IOL. Both share identical pinout, logic function, timing, and package; the -1 version is drop-in compatible where higher sink drive is required - for example, driving heavier capacitive loads or multiple TTL inputs.
SN74ALS642A-IN 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:
- -
SN74ALS642A-IN FAQ
1.How can I place an order for SN74ALS642A-IN through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS642A-IN 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-IN reliable?
The price and inventory of SN74ALS642A-IN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS642A-IN is usually 5 days.
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4.How is shipping managed for SN74ALS642A-IN?
SN74ALS642A-IN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS642A-IN 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-IN?
For technical support, including SN74ALS642A-IN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS642A-IN requirements.
6.How does Aetrix verify that SN74ALS642A-IN is sourced from the original manufacturer or authorized distributors?
All SN74ALS642A-IN 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-IN meets industry standards.
7.What is the process for return or replacement of SN74ALS642A-IN?
All SN74ALS642A-IN units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS642A-IN, 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-IN part is unused and in its original packaging.
Return procedure for SN74ALS642A-IN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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