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Texas Instruments SN74ALS646A-1DWRE4
- Part No.:
- SN74ALS646A-1DWRE4
- Manufacturer:
- Texas Instruments
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS646A-1DWRE4.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,432
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Product details
Overview
SN74ALS646A-1DWRE4 from Texas Instruments is an octal bus transceiver and register IC with 3-state outputs, designed for bidirectional data flow between two 8-bit buses (A and B) in TTL-compatible systems. It features independent A/B registers, real-time or stored data multiplexing via SAB/SBA controls, DIR-controlled direction, OE-enabled 3-state output, and supports up to 40 MHz clock frequency with 48 mA low-level output drive (–1 version). It is used in legacy industrial control backplanes requiring registered bus isolation and glitch-free data switching.
For engineers reviewing the SN74ALS646A-1DWRE4 datasheet, SN74ALS646A-1DWRE4 pinout, SN74ALS646A-1DWRE4 application, or SN74ALS646A-1DWRE4 equivalent, this page delivers verified functional architecture, validated pin mapping for DW package, timing-critical setup/hold constraints, true-data-path behavior (non-inverting), and direct alternatives with documented IOL/VOL/propagation trade-offs - all specific to the –1 speed-grade SOIC-24 variant.
Technical Context
This device integrates dual 8-bit D-type registers (A→B and B→A), synchronous clocking on CLKAB/CLKBA rising edges, and combinational select logic for transparent or stored data routing. Its DIR input determines active bus direction during OE-low operation, while SAB/SBA enable glitch-free multiplexing between live bus data and registered values without decoding hazards.
The –1 suffix denotes enhanced output capability: guaranteed 48 mA IOL at VCC = 4.75–5.25 V, distinct from standard SN74ALS646A (24 mA max). It operates strictly within 0°C to 70°C ambient, uses ALS bipolar technology, and requires no external pull-ups for 3-state control - all parameters confirmed for DW package per SDAS039F Rev. January 1995.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal bus transceiver + dual 8-bit register with 3-state outputs; non-inverting data path |
| Supply Voltage | 4.5 V to 5.5 V - compatible with standard 5 V TTL rails; absolute max 7 V |
| Max Clock Frequency | 40 MHz - enables high-speed bus arbitration in legacy computing and instrumentation |
| IOL (–1 version) | 48 mA - drives heavy capacitive loads or multiple TTL inputs without buffering |
| tPLH / tPHL (A↔B) | 3–20 ns - ensures sub-25 ns bidirectional propagation for synchronous backplane timing |
| Operating Temperature | 0°C to 70°C - commercial-grade rating suitable for enclosed industrial electronics |
| Package | 24-pin SOIC (DW) - surface-mount, RoHS-compliant, moisture-sensitive level 1 |
Pinout & Package
SN74ALS646A-1DWRE4 is housed in a 24-pin SOIC (DW) package, 7.5 mm wide, with standard 1.27 mm pitch. Pin 1 is top-left corner (notch-marked side), pin 24 bottom-right.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | CLKAB | Rising-edge clock for latching data from A bus into B-register |
| 2 | SAB | Select A-to-B: L = real-time A→B; H = stored A→B |
| 3 | DIR | Direction control: L = B→A enabled; H = A→B enabled (when OE = L) |
| 4–11 | A1–A8 | 8-bit data inputs/outputs for A-side bus (bidirectional, 3-state) |
| 12 | GND | Ground reference for all logic and output stages |
| 13 | VCC | Positive supply (4.5–5.5 V); powers internal logic and output drivers |
| 14–21 | B1–B8 | 8-bit data inputs/outputs for B-side bus (bidirectional, 3-state) |
| 22 | SBA | Select B-to-A: L = real-time B→A; H = stored B→A |
| 23 | CLKBA | Rising-edge clock for latching data from B bus into A-register |
| 24 | OE | Output enable: L = transceiver active; H = both A/B ports in high-impedance state |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B registers | Enables simultaneous storage of data from both buses - critical for handshake-free dual-bus buffering |
| Glitch-free multiplexing | SAB/SBA logic eliminates decoding glitches during real-time ↔ stored mode transitions |
| 48 mA IOL (–1 version) | Drives ≥10 standard TTL loads directly - reduces need for external buffers in dense backplanes |
| Real-time + stored data selection | Supports mixed-mode operation: e.g., forward live sensor data while replaying stored calibration values |
| Isolation mode (OE high) | Maintains register contents while disconnecting both buses - preserves state during bus arbitration |
Applications
| Industrial Backplane Interface | Legacy Computer Bus Arbitration |
|---|---|
Use Scenario: Isolating CPU and peripheral modules on a shared 8-bit ISA-style backplane with timing-critical DMA cycles. IC Role / Device Role / Timing Role: Bidirectional registered transceiver managing A (CPU) and B (peripheral) buses; clocks data on CLKAB/CLKBA edges and selects source via SAB/SBA. Use Value: Eliminates bus contention during hot-swap events by holding registered data during OE-high isolation, while supporting 40 MHz burst transfers. |
Use Scenario: Synchronizing memory-mapped I/O between two microcontroller subsystems sharing a common address/data bus. IC Role / Device Role / Timing Role: Acts as a direction-controlled, register-backed bus coupler - DIR sets master/slave role, OE gates access, and registers decouple timing skew. Use Value: Enables deterministic read-modify-write sequences across subsystems using stored data mode, avoiding race conditions on shared lines. |
| Test Equipment Data Capture | Programmable Logic Controller (PLC) I/O Expansion |
Use Scenario: Capturing parallel sensor data streams at 20+ MHz and forwarding time-stamped samples to a controller via a buffered interface. IC Role / Device Role / Timing Role: Registers incoming B-bus sensor data on CLKBA↑, then forwards stored values to A-bus (controller) under SBA control - decoupling capture and readout timing. Use Value: Achieves jitter-free sampling at maximum rated clock (40 MHz) with guaranteed 0 ns hold time, enabling precise timestamp alignment. |
Use Scenario: Extending discrete I/O capacity in modular PLC racks where field devices connect to B-bus and CPU connects to A-bus. IC Role / Device Role / Timing Role: Provides registered, direction-flexible, 3-state-isolated coupling between CPU and expansion modules - DIR selects module read/write, OE enables hot-swap safety. Use Value: Supports safe module insertion/removal (via OE high) while preserving last valid I/O state in registers - prevents spurious actuator triggers. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal registered transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS646ADWR | Same function and pinout, but standard (non–1) version: max IOL = 24 mA, not 48 mA | Lower drive strength limits use in high-fanout or long-trace environments where voltage margin is tight | Select when system load ≤ 24 mA and cost optimization is prioritized over drive headroom |
| SN74AS646DW | Faster (90 MHz fmax), higher ICC (120–211 mA), AS-series Schottky TTL; same DW package and pinout | Higher power consumption and stricter VIH/VIL thresholds (0.8 V VIL) - requires clean 5 V supply and noise-controlled layout | Select for speed-critical designs where propagation delay < 9 ns is mandatory and thermal/power budget allows |
Compared with SN74ALS646A-1DWRE4, SN74ALS646ADWR offers identical functionality at lower output drive, while SN74AS646DW delivers significantly faster timing at the cost of higher power and tighter input threshold compliance - making the –1 variant optimal for robust 40 MHz operation with legacy TTL fanout requirements.
Availability
SN74ALS646A-1DWRE4 is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy computer bus arbitration, and programmable logic controller (PLC) I/O expansion requiring stable component supply, long-lifecycle support, and verified 48 mA drive capability.
Supply support for SN74ALS646A-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 SN74ALS646A-1DWRE4 belongs to TI's legacy ALS (Advanced Low-power Schottky) logic family, engineered for high-speed, low-power 5 V TTL systems requiring registered bus interfacing with robust noise immunity and drive strength.
FAQ
What is the key functional difference between SN74ALS646A-1DWRE4 and the standard SN74ALS646ADWR?
The SN74ALS646A-1DWRE4 guarantees 48 mA low-level output current (IOL) when VCC is maintained between 4.75 V and 5.25 V, whereas the standard SN74ALS646ADWR is rated for only 24 mA IOL. This makes the –1 version suitable for driving heavier TTL loads or longer traces without signal degradation, while maintaining identical pinout, timing, and logic functionality.
Does SN74ALS646A-1DWRE4 support inverting data paths like SN74ALS648A?
No. SN74ALS646A-1DWRE4 implements a true (non-inverting) data path, as confirmed in the device description and function tables. SN74ALS648A is the inverting counterpart in the same family - they share pinout and package but differ in output polarity and are not functionally interchangeable without logic redesign.
What is the purpose of the SAB and SBA pins on SN74ALS646A-1DWRE4?
SAB (Select A-to-B) and SBA (Select B-to-A) control whether real-time bus data or previously registered data is routed across the transceiver. When SAB = L, real-time A-bus data flows to B; when SAB = H, stored A-register data flows to B - eliminating multiplexer glitches during mode transitions, a key reliability feature of SN74ALS646A-1DWRE4.
Can SN74ALS646A-1DWRE4 operate outside the 0°C to 70°C range?
No. SN74ALS646A-1DWRE4 is characterized and specified only for 0°C to 70°C free-air operating temperature. Military-grade variants (e.g., SN54ALS646) support –55°C to 125°C, but the –1 suffix and DW package are exclusive to the commercial-grade SN74ALS646A series - operation outside 0–70°C voids parametric guarantees.
How does the DIR pin affect data flow when OE is high on SN74ALS646A-1DWRE4?
When OE is high, both A and B ports are in high-impedance state regardless of DIR setting - no data is driven onto either bus. However, DIR remains active internally: it continues to determine which register (A or B) captures data on subsequent CLKAB↑ or CLKBA↑ edges, allowing pre-loading of registers during isolation for immediate transfer once OE is asserted low.
SN74ALS646A-1DWRE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 24-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Logic Type:
- Transceiver, Non-Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- -
- Output Type:
- 3-State
- Current - Output High, Low:
- 15mA, 24mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-SOIC
SN74ALS646A-1DWRE4 FAQ
1.How can I place an order for SN74ALS646A-1DWRE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS646A-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 SN74ALS646A-1DWRE4 reliable?
The price and inventory of SN74ALS646A-1DWRE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS646A-1DWRE4 is usually 5 days.
3.What payment methods are accepted for SN74ALS646A-1DWRE4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS646A-1DWRE4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS646A-1DWRE4?
SN74ALS646A-1DWRE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS646A-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 SN74ALS646A-1DWRE4?
For technical support, including SN74ALS646A-1DWRE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS646A-1DWRE4 requirements.
6.How does Aetrix verify that SN74ALS646A-1DWRE4 is sourced from the original manufacturer or authorized distributors?
All SN74ALS646A-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 SN74ALS646A-1DWRE4 meets industry standards.
7.What is the process for return or replacement of SN74ALS646A-1DWRE4?
All SN74ALS646A-1DWRE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS646A-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 SN74ALS646A-1DWRE4 part is unused and in its original packaging.
Return procedure for SN74ALS646A-1DWRE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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