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Texas Instruments SN74ALS651A-1DWR
- Part No.:
- SN74ALS651A-1DWR
- Manufacturer:
- Texas Instruments
- Package:
- -
- Datasheet:
-
SN74ALS651A-1DWR.pdf
- Description:
- BUS TRANSCEIVER, ALS SERIES
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Inventory:6,000
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Product details
Overview
SN74ALS651A-1DWR from Texas Instruments is an octal bus transceiver and register IC with inverting data path, 3-state outputs on both A and B buses, and dual clock/register control (CLKAB/CLKBA). It supports real-time or stored data transfer via SAB/SBA select inputs, operates at up to 40 MHz, and delivers 48 mA low-level output current (–1 version) for driving heavy TTL loads in industrial backplane and memory interface applications.
For engineers reviewing the SN74ALS651A-1DWR datasheet, SN74ALS651A-1DWR pinout, SN74ALS651A-1DWR application, or SN74ALS651A-1DWR equivalent, this device is selected for bidirectional bus isolation with storage capability, glitch-free multiplexed data routing, and compatibility with legacy ALS logic families requiring high sink drive and precise timing control.
Technical Context
The SN74ALS651A-1DWR integrates eight independent D-type flip-flops with dual-directional 3-state transceivers, enabling simultaneous or selective latching of data from either A or B bus. Its select-control logic eliminates decoding glitches during transitions between real-time and stored modes - a low SAB/SBA selects real-time transfer, while high enables registered output.
It features independent OEAB/OEBA enables for per-bus output control and supports four fundamental bus-management functions: isolation, real-time A↔B transfer, storage from A/B, and concurrent delivery of stored data to both buses - all without external decoding logic.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | ALS (Advanced Low-Power Schottky), compatible with TTL voltage levels and noise margins |
| Max Clock Frequency | 40 MHz - supports high-speed synchronous bus arbitration in legacy computing systems |
| IOL (–1 version) | 48 mA at VCC = 4.75–5.25 V - drives multiple TTL inputs or long traces without buffering |
| Propagation Delay | tPLH/tPHL ≤ 32 ns (CLK→A/B); ≤ 18 ns (A/B→A/B) - ensures tight timing closure in 25 ns cycle designs |
| Output Type | 3-state on both A and B ports - enables shared bus contention management and hot-swap isolation |
| Operating Temperature | 0°C to +70°C - qualified for commercial-grade embedded control and instrumentation environments |
| Supply Voltage | 4.5 V to 5.5 V - robust against rail droop in noisy power domains typical of industrial PCBs |
Pinout & Package
SN74ALS651A-1DWR uses a 24-pin SOIC (DW) package with standard pinout per TI SDAS066G Rev. December 2000. Pin numbering follows top-view orientation with pin 1 at bottom-left corner.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | CLKBA | Clock input for B→A register latch; rising edge captures B-bus data into internal flip-flops |
| 2 | SAB | Select input: low = real-time B→A transfer, high = stored B→A output |
| 3 | OEAB | Output enable for A-bus drivers; low = active, high = high-impedance |
| 4–11 | A1–A8 | 8-bit bidirectional I/O port A - connects to system address/data bus segment |
| 12 | GND | Ground reference for all logic and I/O circuits |
| 13 | VCC | +5 V supply input - decoupling required within 1 cm of pin |
| 14 | CLKAB | Clock input for A→B register latch; rising edge captures A-bus data |
| 15 | SBA | Select input: low = real-time A→B transfer, high = stored A→B output |
| 16 | OEBA | Output enable for B-bus drivers; low = active, high = high-impedance |
| 17–24 | B1–B8 | 8-bit bidirectional I/O port B - interfaces to peripheral or memory bus segment |
Key Features
| Feature | Design Value |
|---|---|
| Inverting data path | Outputs complement input data - used for polarity correction or differential signaling prep |
| Glitch-free select control | Internal logic prevents metastability during SAB/SBA transitions - eliminates need for external synchronizers |
| Dual-clock register architecture | Independent CLKAB and CLKBA allow asynchronous capture from A and B buses without conflict |
| Simultaneous real-time + stored operation | Enables concurrent A→B real-time transfer while delivering stored B→A data - supports full-duplex bus bridging |
| High-current –1 output variant | 48 mA IOL rating sustains signal integrity across 50 Ω transmission lines or 10+ TTL loads |
Applications
| Backplane Bus Arbitration | Legacy Memory Interface |
|---|---|
|
Use Scenario: Isolating and multiplexing address/data traffic between CPU and multiple plug-in cards in a VME or Multibus-style chassis. IC Role / Device Role / Timing Role: Bidirectional transceiver and register managing A-bus (CPU side) and B-bus (card side) with selectable real-time or buffered transfer. Use Value: Eliminates external glue logic by integrating clocked storage and 3-state control - reduces board area and improves timing predictability. |
Use Scenario: Interfacing a microprocessor to dual-port RAM or ROM banks with separate read/write strobes and address latching. IC Role / Device Role / Timing Role: Latches address bits on CLKAB, holds data on CLKBA, and routes stored values to memory control lines via SAB/SBA selection. Use Value: Enables zero-wait-state memory access using stored addresses while CPU executes other instructions - increases effective throughput. |
| Industrial PLC I/O Expansion | Test Equipment Signal Routing |
|
Use Scenario: Expanding digital I/O capacity in programmable logic controllers where field-side signals must be isolated, conditioned, and synchronized with scan cycles. IC Role / Device Role / Timing Role: Captures sensor/actuator states on B-bus at scan start (CLKBA↑), then outputs registered values to CPU A-bus under OEAB control. Use Value: Provides deterministic sampling window and eliminates metastability risk from asynchronous field inputs - meets IEC 61131-3 timing requirements. |
Use Scenario: Reconfigurable signal path switching in automated test equipment (ATE), routing stimulus or measurement signals between DUT and instruments. IC Role / Device Role / Timing Role: Stores instrument output patterns (B-bus), then delivers them to DUT inputs (A-bus) under precise trigger timing via CLKAB and OEAB. Use Value: Supports pattern-based testing with sub-25 ns setup/hold margins - enables 40 MHz vector rate without FPGA overhead. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver and register applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS652A-1DWR | True (non-inverting) data path; otherwise identical pinout, timing, and drive strength | Used where signal polarity preservation is required - e.g., direct connection to non-inverting bus drivers or level translators | Select when inverting logic would require additional gates or complicate timing analysis |
| SN74AS651DWR | Faster propagation (≤18 ns), higher IOL (48 mA), but AS family consumes more power (ICC ≈ 110 mA vs. 76 mA) | Suitable for high-speed test fixtures or military-grade systems needing extended frequency margin beyond 40 MHz | Choose only if speed gain justifies 45% higher quiescent current and stricter layout controls for noise suppression |
Compared with SN74ALS651A-1DWR, SN74ALS652A-1DWR provides identical functionality with true logic polarity, simplifying integration where inversion is undesirable; SN74AS651DWR trades higher power for faster switching and broader fanout capability - making it viable only when 40 MHz timing margin is insufficient.
Availability
SN74ALS651A-1DWR is available at Aetrix Electronics and suitable for industrial backplane design, legacy memory subsystems, and programmable controller I/O expansion requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS651A-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 founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The SN74ALS651A-1DWR belongs to TI's legacy ALS logic portfolio, engineered for backward compatibility with 1980s-era computing and control systems while maintaining reliability under sustained thermal and electrical stress.
FAQ
What is the key functional difference between SN74ALS651A-1DWR and SN74ALS652A-1DWR?
The SN74ALS651A-1DWR implements an inverting data path between A and B buses, while SN74ALS652A-1DWR provides a true (non-inverting) path. Both share identical pinout, timing specs, 48 mA IOL rating, and register/transceiver architecture. This inversion affects signal polarity handling - SN74ALS651A-1DWR is selected when downstream logic expects complemented data, avoiding extra inverters.
Does SN74ALS651A-1DWR support simultaneous real-time and stored data transfer?
Yes. The SN74ALS651A-1DWR can deliver stored data from one bus while passing real-time data from the other - for example, outputting registered B-bus data to A-bus (SAB = H, OEAB = L) while simultaneously transferring real-time A-bus data to B-bus (SBA = L, OEBA = L). This full-duplex capability is enabled by independent select and enable controls per bus.
What is the significance of the "–1" suffix in SN74ALS651A-1DWR?
The "–1" suffix denotes the enhanced-output version of SN74ALS651A, specifying a guaranteed minimum low-level output current (IOL) of 48 mA when VCC is maintained between 4.75 V and 5.25 V. Standard SN74ALS651A guarantees only 24 mA IOL. This higher drive supports heavier capacitive loads or longer traces without signal degradation.
Can SN74ALS651A-1DWR operate with mixed-voltage buses (e.g., 3.3 V A-bus and 5 V B-bus)?
No. The SN74ALS651A-1DWR is a 5 V-only device with absolute maximum I/O voltage of 5.5 V. Its inputs are TTL-compatible (VIH = 2 V, VIL = 0.8 V), but connecting to a 3.3 V bus risks violating the minimum VIH threshold and may cause unreliable logic detection. Level-shifting circuitry is required for interfacing with sub-5 V buses.
How does the glitch-free select control in SN74ALS651A-1DWR improve system reliability?
The SN74ALS651A-1DWR uses internal synchronous logic to prevent metastability during SAB/SBA transitions, eliminating the decoding glitches common in discrete multiplexer implementations. This ensures clean, deterministic bus handoff between real-time and stored modes - critical in safety-critical PLC scan cycles or memory refresh sequences where transient bus contention could corrupt data.
SN74ALS651A-1DWR 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:
- -
SN74ALS651A-1DWR FAQ
1.How can I place an order for SN74ALS651A-1DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS651A-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 SN74ALS651A-1DWR reliable?
The price and inventory of SN74ALS651A-1DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS651A-1DWR is usually 5 days.
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SN74ALS651A-1DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS651A-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 SN74ALS651A-1DWR?
For technical support, including SN74ALS651A-1DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS651A-1DWR requirements.
6.How does Aetrix verify that SN74ALS651A-1DWR is sourced from the original manufacturer or authorized distributors?
All SN74ALS651A-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 SN74ALS651A-1DWR meets industry standards.
7.What is the process for return or replacement of SN74ALS651A-1DWR?
All SN74ALS651A-1DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS651A-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 SN74ALS651A-1DWR part is unused and in its original packaging.
Return procedure for SN74ALS651A-1DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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