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Texas Instruments SN74ALS642A-1DWRE4
- Part No.:
- SN74ALS642A-1DWRE4
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS642A-1DWRE4.pdf
- Description:
- IC TXRX INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,517
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Product details
Overview
SN74ALS642A-1DWRE4 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. 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 and board-to-board communication systems requiring level-shifting isolation.
For engineers reviewing the SN74ALS642A-1DWRE4 datasheet, SN74ALS642A-1DWRE4 pinout, SN74ALS642A-1DWRE4 application, or SN74ALS642A-1DWRE4 equivalent, key selection criteria include its inverting logic function, -1 version's enhanced 48 mA sink capability, SOIC-20 thermal and layout constraints, and compatibility with ALS-family timing and voltage thresholds.
Technical Context
This device implements true bidirectional data flow controlled by DIR: when DIR = L, B-bus data propagates to A-bus; when DIR = H, A-bus data propagates to B-bus. OE independently disables both directions into high-impedance state, enabling bus isolation without external gating.
It belongs to the 74ALS logic family and uses bipolar Schottky technology, delivering propagation delays of 5–30 ns (tPLH/tPHL) under 50 pF load and 680 Ω termination, with guaranteed VOL ≤ 0.5 V at IOL = 48 mA and VIH/VIL thresholds of 2.0 V/0.8 V respectively.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Function | Inverting bidirectional bus transceiver with DIR/OE control |
| Supply Voltage (VCC) | 4.5 V to 5.5 V - compatible with standard 5 V TTL systems |
| Output Drive (IOL) | 48 mA - supports driving heavier loads than standard ALS (24 mA), critical for stub-loaded backplanes |
| Propagation Delay | 5–30 ns - ensures timing compliance in synchronous bus architectures up to ~20 MHz |
| Operating Temperature | 0°C to 70°C - qualified for commercial/industrial ambient environments |
| Input Thresholds | VIH = 2.0 V, VIL = 0.8 V - matches TTL input compatibility without level translation |
| VOL @ IOL=48 mA | ≤ 0.5 V - guarantees robust low-state noise margin under full drive |
Pinout & Package
SN74ALS642A-1DWRE4 is housed in a 20-pin SOIC (DW) package, 7.5 mm wide, 12.83 mm long, 2.65 mm max height, with 1.27 mm pitch, RoHS-compliant NiPdAu lead finish, and MSL Level-1 rating.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 19 | DIR (Direction Control) | Active-High signal selecting A→B (H) or B→A (L) data path; determines signal polarity inversion direction |
| 2, 18 | OE (Output Enable) | Active-Low control disabling both A and B ports to high-Z - essential for bus arbitration and hot-swap isolation |
| 3–10 | A1–A8 | Octal bidirectional I/O port A - connects to local processor/data bus; driven or received depending on DIR state |
| 11–18 | B1–B8 | Octal bidirectional I/O port B - interfaces to remote bus segment; data polarity inverted relative to A-port per function table |
| 9 | GND | Power ground reference - requires low-inductance connection to minimize switching noise coupling |
| 20 | VCC | +5 V supply - must be decoupled locally with 0.1 µF ceramic capacitor near pin |
Key Features
| Feature | Design Value |
|---|---|
| Inverting Transceiver Logic | Ensures signal polarity inversion across A↔B paths - required in legacy systems where bus topology mandates complementary signaling |
| 48 mA Output Sink Capability (-1 version) | Enables direct interface to multiple TTL inputs or resistive loads without external buffers, reducing component count |
| High-Z Isolation via OE | Prevents bus contention during power-up, reset, or fault conditions - critical for multi-master system reliability |
| TTL-Compatible Input Thresholds | Eliminates need for level shifters when interfacing with 74LS/74ALS/74AS families, simplifying mixed-logic designs |
| SOIC-20 Package with MSL-1 Rating | Supports standard reflow assembly without moisture sensitivity concerns, suitable for high-volume manufacturing |
Applications
| Industrial Backplane Interface | Legacy System Bus Expansion |
|---|---|
Use Scenario: Interfacing microcontroller local bus to extended ISA-style backplane with distributed peripherals. IC Role / Device Role / Timing Role: Bidirectional data bridge that inverts signals per backplane specification while isolating segments during configuration cycles. Use Value: Enables reuse of existing 74ALS-based backplane wiring without redesign; 48 mA drive sustains signal integrity over 15 cm traces with 5–7 stubs. | Use Scenario: Adding memory-mapped I/O expansion to vintage 8-bit embedded controllers (e.g., Z80, 8085). IC Role / Device Role / Timing Role: Direction-controlled transceiver managing data flow between CPU address/data bus and peripheral register banks. Use Value: DIR and OE allow precise cycle-by-cycle control of read/write handshaking; inverting logic matches legacy peripheral timing diagrams. |
| Test Equipment Data Routing | Programmable Logic Interconnect |
Use Scenario: Signal routing matrix in automated test equipment (ATE) switching between DUT channels and measurement units. IC Role / Device Role / Timing Role: Configurable bidirectional channel element controlled by FPGA logic for dynamic path assignment. Use Value: High-Z isolation prevents leakage between unselected paths; 30 ns max delay supports 10 MHz pattern rates with setup/hold margin. | Use Scenario: Glue logic between CPLD/FPGA I/O banks and external parallel devices (e.g., ADCs, DACs, SRAM). IC Role / Device Role / Timing Role: Level-translating and direction-managed interface ensuring timing-aligned data capture across logic domains. Use Value: Matches 74ALS voltage thresholds to avoid metastability; OE synchronization allows clean domain crossing under clock domain control. |
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 with 24 mA IOL (vs. 48 mA in -1); identical pinout, timing, and logic function | Suitable for lighter loads (< 4 TTL inputs); lower power consumption but reduced noise immunity on long traces | Select when drive strength requirements are met by 24 mA and cost optimization is prioritized |
| SN74AS641DW | Faster propagation (1–10 ns vs. 3–30 ns), higher ICC (50–136 mA), non-inverting logic, 64 mA IOL | Used where speed > 25 MHz is required; incompatible polarity necessitates PCB or firmware logic inversion | Choose only if timing budget demands sub-15 ns delays and system can accommodate true (non-inverting) data path |
Compared with SN74ALS642ADWR, the SN74ALS642A-1DWRE4 delivers double the output sink current for improved noise margin on loaded buses; compared with SN74AS641DW, it trades speed for lower power and maintains inverting logic required by legacy bus protocols.
Availability
SN74ALS642A-1DWRE4 is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus expansion, test equipment data routing, and programmable logic interconnect requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS642A-1DWRE4 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-1DWRE4 belongs to TI's legacy 74ALS logic family, engineered for reliable, low-power bidirectional bus communication in commercial-temperature industrial control and instrumentation systems.
FAQ
What is the key functional difference between SN74ALS642A-1DWRE4 and the standard SN74ALS642A?
The SN74ALS642A-1DWRE4 is the "-1" variant, distinguished by its increased low-level output current rating of 48 mA (vs. 24 mA for the standard version), specified only when VCC is between 4.75 V and 5.25 V. All other electrical characteristics, pinout, logic function, and package are identical. This enhanced drive supports longer traces or heavier capacitive loads in legacy bus systems.
Does SN74ALS642A-1DWRE4 support hot-swapping or live insertion?
The SN74ALS642A-1DWRE4 does not include built-in hot-swap protection features such as power-on reset, slew-rate control, or undervoltage lockout. However, its three-state outputs (enabled by OE) allow safe bus isolation during insertion if OE is held active-low until power and control signals stabilize. External circuitry is required for full hot-swap compliance.
Can SN74ALS642A-1DWRE4 be used with 3.3 V logic systems?
No - SN74ALS642A-1DWRE4 is strictly a 5 V device with VCC min/max of 4.5 V–5.5 V and TTL-compatible input thresholds (VIH = 2.0 V, VIL = 0.8 V). Driving its inputs from 3.3 V logic may result in marginal or unreliable high-level recognition. A level-shifting buffer or voltage translator is required for interoperability with 3.3 V systems.
What is the maximum capacitive load SN74ALS642A-1DWRE4 can drive while maintaining timing specifications?
The switching characteristics (tPLH/tPHL) in the datasheet are characterized at CL = 50 pF. While the device can physically drive higher capacitance, propagation delay increases linearly with load; exceeding 50 pF degrades timing margins and may violate setup/hold windows in synchronous systems. For loads > 50 pF, derating analysis or empirical validation is required.
Is SN74ALS642A-1DWRE4 pin-compatible with SN74ALS641A-1DWRE4?
Yes - SN74ALS642A-1DWRE4 and SN74ALS641A-1DWRE4 share identical 20-pin SOIC (DW) packages and pinouts, including DIR, OE, A1–A8, B1–B8, VCC, and GND locations. The sole functional difference is logic polarity: SN74ALS642A-1DWRE4 is inverting, while SN74ALS641A-1DWRE4 is true. Swapping them requires firmware or schematic logic inversion.
SN74ALS642A-1DWRE4 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-1DWRE4 FAQ
1.How can I place an order for SN74ALS642A-1DWRE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS642A-1DWRE4 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-1DWRE4 reliable?
The price and inventory of SN74ALS642A-1DWRE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS642A-1DWRE4 is usually 5 days.
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SN74ALS642A-1DWRE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS642A-1DWRE4 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-1DWRE4?
For technical support, including SN74ALS642A-1DWRE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS642A-1DWRE4 requirements.
6.How does Aetrix verify that SN74ALS642A-1DWRE4 is sourced from the original manufacturer or authorized distributors?
All SN74ALS642A-1DWRE4 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-1DWRE4 meets industry standards.
7.What is the process for return or replacement of SN74ALS642A-1DWRE4?
All SN74ALS642A-1DWRE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS642A-1DWRE4, 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-1DWRE4 part is unused and in its original packaging.
Return procedure for SN74ALS642A-1DWRE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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