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Texas Instruments SN74ALS642A-1DWR
- Part No.:
- SN74ALS642A-1DWR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS642A-1DWR.pdf
- Description:
- IC TXRX INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,169
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Product details
Overview
SN74ALS642A-1DWR from Texas Instruments is an octal inverting bidirectional bus transceiver in a 20-pin SOIC (DW) package, designed for asynchronous two-way data transfer between A and B buses with direction control via DIR and isolation via OE. It supports 5-V operation, delivers 48 mA low-level output current (IOL), and operates across 0°C to 70°C for industrial bus interfacing.
For engineers reviewing the SN74ALS642A-1DWR datasheet, SN74ALS642A-1DWR pinout, SN74ALS642A-1DWR application, or SN74ALS642A-1DWR equivalent, key selection criteria include its inverting logic function, 30 ns max propagation delay (tPHL/tPLH), 48 mA drive capability in the -1 version, and compatibility with legacy TTL/ALS bus systems requiring isolated bidirectional data routing.
Technical Context
The SN74ALS642A-1DWR implements true inverting transceiver logic: data flows from A to B when DIR = HIGH, and from B to A when DIR = LOW; OE = HIGH disables all outputs into high-impedance state. Its internal architecture uses bipolar ALS (Advanced Low-Power Schottky) technology, delivering higher speed and lower power than standard LS logic while maintaining TTL-compatible voltage thresholds.
It features dual 8-bit I/O ports (A1–A8 and B1–B8), shared control inputs (DIR and OE), and is characterized for 4.5 V to 5.5 V supply operation. The -1 suffix denotes enhanced output drive-specifically, guaranteed 48 mA IOL at VCC = 4.75–5.25 V-enabling direct interface with heavier capacitive loads or multiple downstream receivers without external buffers.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - Ensures stable operation across standard 5-V TTL/ALS supply tolerances. |
| IOL (max) | 48 mA - Enables driving 10+ standard TTL loads or long PCB traces without signal degradation. |
| tPHL/tPLH (max) | 30 ns - Supports bus clock rates up to ~16 MHz in point-to-point configurations. |
| VIL/VIH | 0.8 V / 2.0 V - Fully compatible with TTL input thresholds for seamless integration into legacy systems. |
| Operating Temp | 0°C to 70°C - Qualified for commercial and industrial ambient environments without derating. |
| VOL @ IOL=48 mA | 0.5 V max - Maintains valid LOW logic level even under full output sink current. |
| ICC (active) | 15 mA max (outputs high) - Low quiescent power vs. AS-series alternatives, reducing thermal load in dense layouts. |
Pinout & Package
SN74ALS642A-1DWR is housed in a 20-pin SOIC (DW) package per JEDEC MS-013, 7.5 mm body width, 2.65 mm max height, 1.27 mm lead pitch, and gull-wing surface-mount leads.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 19 | DIR (Direction Control) | Active-HIGH input: enables A→B data flow; LOW enables B→A. Critical for bus arbitration timing. |
| 2, 18 | OE (Output Enable) | Active-LOW input: disables all A/B outputs to high-Z; essential for bus sharing and hot-swap isolation. |
| 3–10 | A1–A8 | Octal bidirectional I/O port - connects to local CPU/memory bus; driven by internal inverting transceiver core. |
| 11–18 | B1–B8 | Octal bidirectional I/O port - connects to peripheral/remote bus; complements A-port with inverted data path. |
| 9 | GND | Ground reference for all logic and output stages; requires low-impedance PCB plane connection. |
| 20 | VCC | +5 V supply; bypassing with 0.1 µF ceramic capacitor near pin is mandatory for noise immunity. |
Key Features
| Feature | Design Value |
|---|---|
| Inverting transceiver logic | Ensures signal polarity inversion across A↔B paths, required for specific backplane and daisy-chain topologies. |
| 48 mA output sink capability (-1 version) | Eliminates need for external buffer stages when driving high-capacitance buses or multiple TTL inputs. |
| 3-State outputs with common OE | Allows multiple transceivers to share same A or B bus without contention; OE timing directly affects bus turnaround latency. |
| TTL-compatible input thresholds | Supports direct connection to legacy 74LS/74ALS devices without level-shifting circuitry. |
| ALS process technology | Delivers 2× speed and 50% lower power vs. standard LS, enabling denser bus interface designs. |
Applications
| Industrial Backplane Interfacing | Legacy System Bus Extension |
|---|---|
Use Scenario: Connecting microcontroller local bus to a multi-slot industrial backplane carrying sensor/actuator data. IC Role / Device Role / Timing Role: Bidirectional bus isolator and level translator between CPU subsystem and extended peripheral chassis. Use Value: 48 mA drive ensures reliable signal integrity over 15 cm backplane traces; DIR-controlled flow prevents bus collisions during hot-plug events. | Use Scenario: Extending an aging 8-bit ISA-style bus to add new I/O cards while preserving original controller firmware. IC Role / Device Role / Timing Role: Inverting transceiver bridging legacy CPU address/data bus to new peripheral expansion segment. Use Value: TTL-compatible thresholds and 30 ns propagation enable drop-in replacement without timing revalidation of existing ISA timing budgets. |
| Programmable Logic Interface | Test Equipment Data Routing |
Use Scenario: Interfacing FPGA I/O banks to external memory or peripheral ASICs with mismatched voltage swing or drive strength. IC Role / Device Role / Timing Role: Direction-controlled data conduit between configurable logic and fixed-function hardware blocks. Use Value: OE-controlled isolation allows FPGA to safely reconfigure while holding bus in known state; inverting logic matches certain PLD output conventions. | Use Scenario: Automated test equipment switching measurement signals between DUT channels and digitizer inputs. IC Role / Device Role / Timing Role: Reconfigurable signal path selector using DIR/OE to route analog/digital stimulus/response lines. Use Value: 0.5 V VOL at 48 mA guarantees clean LOW detection in high-noise test environments; SOIC package supports automated optical inspection. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar bidirectional bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS642ADWR | Standard version: rated for 24 mA IOL, not 48 mA; otherwise identical pinout, timing, and logic function. | Suitable only where bus loading is light (< 5 TTL loads) or where margin for aging/supply variation is sufficient. | Select SN74ALS642ADWR only if system-level validation confirms 24 mA drive meets worst-case noise and rise-time requirements. |
| SN74AS641DW | True (non-inverting) logic, higher speed (7.5 ns tPHL), higher power (136 mA ICC), 64 mA IOL; same pinout but different truth table. | Requires redesign of DIR control logic and verification of setup/hold timing due to faster edges and different polarity behavior. | Choose SN74AS641DW only when speed is critical and inverting logic is not required; verify PCB trace impedance and decoupling for AS-series EMI. |
Compared with SN74ALS642ADWR, the SN74ALS642A-1DWR provides double the output sink current for robustness on loaded buses; compared with SN74AS641DW, it trades raw speed for lower power and inverting functionality-making it optimal for cost-sensitive, noise-resilient industrial bus extensions where polarity alignment matters.
Availability
SN74ALS642A-1DWR is available at Aetrix Electronics and suitable for industrial backplane interfacing, legacy system bus extension, programmable logic interface, and test equipment data routing requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS642A-1DWR 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 specializing in analog, embedded processing, and logic solutions with over 50 years of innovation in industrial, automotive, and communications markets.
The SN74ALS642A-1DWR belongs to TI's legacy 74ALS logic family, engineered for high-reliability, medium-speed bidirectional bus communication in commercial and industrial systems where power efficiency and TTL compatibility are prioritized over maximum speed.
FAQ
What logic function does the SN74ALS642A-1DWR implement?
The SN74ALS642A-1DWR implements an inverting bidirectional bus transceiver function: when DIR = HIGH, data transfers from A to B with inversion; when DIR = LOW, data transfers from B to A with inversion. This differs from the true-logic SN74ALS641A series. The SN74ALS642A-1DWR maintains this behavior across its full operating range of 0°C to 70°C and 4.5 V to 5.5 V supply.
How does the "-1" suffix affect the SN74ALS642A-1DWR's electrical specifications?
The "-1" suffix on SN74ALS642A-1DWR specifies an enhanced output drive rating: guaranteed 48 mA low-level output current (IOL) when VCC is between 4.75 V and 5.25 V. Standard SN74ALS642A parts are rated for only 24 mA IOL. All other parameters-including propagation delay, voltage thresholds, and pinout-remain identical between -1 and non--1 versions.
Is the SN74ALS642A-1DWR pin-compatible with SN74ALS641A-1DWR?
Yes, the SN74ALS642A-1DWR is pin-compatible with SN74ALS641A-1DWR: both use the same 20-pin SOIC (DW) package and share identical pin assignments for DIR, OE, A1–A8, B1–B8, VCC, and GND. However, their logic functions differ-SN74ALS641A is true (non-inverting), while SN74ALS642A-1DWR is inverting-so firmware or control logic must be verified for functional correctness after substitution.
What is the maximum recommended capacitive load for the SN74ALS642A-1DWR outputs?
The SN74ALS642A-1DWR's switching characteristics (tPLH, tPHL) are specified with CL = 50 pF and RL = 680 Ω. While not explicitly rated beyond that, empirical design practice limits total load capacitance-including PCB trace, connector, and input capacitance of downstream devices-to ≤75 pF to maintain timing margins and avoid excessive rise/fall time degradation. Exceeding this may require adding series termination or reducing trace length.
Does the SN74ALS642A-1DWR support hot-swap or live-insertion on a powered bus?
The SN74ALS642A-1DWR is not specifically qualified for hot-swap operation. Its absolute maximum ratings allow VI up to 7 V on I/O pins, but no built-in bus-fault protection, current limiting, or power-up sequencing control is provided. For live-insertion, external series resistors (e.g., 10–33 Ω) and careful OE timing coordination are required to prevent bus contention transients. Always assert OE HIGH before applying VCC during hot insertion.
SN74ALS642A-1DWR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- 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:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74ALS642A-1DWR FAQ
1.How can I place an order for SN74ALS642A-1DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS642A-1DWR 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-1DWR reliable?
The price and inventory of SN74ALS642A-1DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS642A-1DWR is usually 5 days.
3.What payment methods are accepted for SN74ALS642A-1DWR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS642A-1DWR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS642A-1DWR?
SN74ALS642A-1DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS642A-1DWR 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-1DWR?
For technical support, including SN74ALS642A-1DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS642A-1DWR requirements.
6.How does Aetrix verify that SN74ALS642A-1DWR is sourced from the original manufacturer or authorized distributors?
All SN74ALS642A-1DWR 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-1DWR meets industry standards.
7.What is the process for return or replacement of SN74ALS642A-1DWR?
All SN74ALS642A-1DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS642A-1DWR, 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-1DWR part is unused and in its original packaging.
Return procedure for SN74ALS642A-1DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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