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Texas Instruments SN74ALS651A-1NT
- Part No.:
- SN74ALS651A-1NT
- Manufacturer:
- Texas Instruments
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- -
- Datasheet:
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SN74ALS651A-1NT.pdf
- Description:
- BUS TRANSCEIVER, ALS SERIES
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Product details
Overview
SN74ALS651A-1NT from Texas Instruments is an octal bus transceiver and register IC with inverting 3-state outputs on both A and B buses, designed for bidirectional data multiplexing in legacy TTL-based systems. It supports real-time or stored data transfer, features independent clock and select controls (CLKAB/CLKBA, SAB/SBA), and delivers 48 mA low-level output drive at VCC = 4.75–5.25 V - used in industrial backplane interfaces and vintage computer bus arbitration.
For engineers reviewing the SN74ALS651A-1NT datasheet, SN74ALS651A-1NT pinout, SN74ALS651A-1NT application, or SN74ALS651A-1NT equivalent, key selection criteria include its inverting logic path, dual-register storage capability, -1 version's enhanced IOL rating, and compatibility with 5-V ALS logic families in space-constrained PDIP-24 designs.
Technical Context
The SN74ALS651A-1NT integrates eight D-type flip-flops with dual-bus transceiver circuitry, enabling simultaneous or selective latching of A- and B-bus data via CLKAB and CLKBA inputs. Its select-control logic (SAB/SBA) eliminates multiplexer glitches during real-time ↔ stored data transitions, with low = real-time and high = stored mode.
Output-enable inputs OEAB and OEBA independently control 3-state drivers on each bus, while internal storage registers retain data even when outputs are disabled. The device operates strictly at 5 V (4.5–5.5 V), conforms to ALS logic thresholds (VIH = 2 V, VIL = 0.8 V), and supports up to 40 MHz clock frequency under loaded conditions (CL = 50 pF).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | Advanced Low-Power Schottky (ALS), TTL-compatible input/output levels |
| Bus Direction | Bidirectional with independent A↔B transceiver and register control |
| Output Type | Inverting 3-state outputs on both A and B ports - enables bus contention avoidance |
| Max IOL (-1 version) | 48 mA at VCC = 4.75–5.25 V - supports driving heavier loads than standard ALS |
| Max Clock Frequency | 40 MHz - defines maximum data throughput rate for synchronous register updates |
| Propagation Delay | tPLH/tPHL ≤ 32/17 ns (CLK→bus); tPZH/tPHZ ≤ 20/9 ns (OE→output enable/disable) |
| Operating Temperature | 0°C to +70°C - commercial-grade rating suitable for non-military embedded systems |
Pinout & Package
SN74ALS651A-1NT is housed in a 24-pin plastic dual in-line package (PDIP-24, NT suffix), with 67°C/W thermal resistance and through-hole mounting. Pin numbering follows JEDEC MS-001 standard for NT packages.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2 | CLKAB, SAB | Active-high clock and select for A→B data path; SAB = L → real-time A-to-B transfer |
| 3, 23 | OEAB, OEBA | Independent 3-state enables: OEAB = L enables A outputs; OEBA = L enables B outputs |
| 4–11 | A1–A8 | Inverting 3-state data outputs/inputs for A bus - driven by stored or real-time data |
| 12 | GND | Power ground reference for all logic and I/O circuits |
| 13 | VCC | +5 V supply (4.5–5.5 V) - powers internal registers, logic, and output drivers |
| 14, 24 | CLKBA, SBA | Active-high clock and select for B→A data path; SBA = L → real-time B-to-A transfer |
| 15–22 | B1–B8 | Inverting 3-state data outputs/inputs for B bus - synchronized with CLKBA/SBA |
Key Features
| Feature | Design Value |
|---|---|
| Glitch-free select control | Eliminates transient bus contention during real-time ↔ stored data switching via synchronized SAB/SBA logic |
| Dual independent registers | Separate CLKAB/CLKBA inputs allow asynchronous latching of A- and B-bus data into distinct storage banks |
| Inverting data path | Ensures signal polarity consistency across bus domains when interfacing with complementary logic stages |
| High-drive -1 variant | 48 mA IOL rating enables direct interface with legacy TTL loads without external buffers |
| Real-time reinforcement mode | Simultaneous OEAB = OEBA = L configures transceivers as bus repeaters - maintains bus state without register involvement |
Applications
| Industrial Backplane Interface | Legacy Computer Bus Arbitration |
|---|---|
Use Scenario: Isolating and routing data between CPU, memory, and I/O modules on a 1980s-style industrial backplane using shared address/data lines. IC Role / Device Role / Timing Role: Octal transceiver/register providing bidirectional, glitch-free data handoff between bus masters with local storage for handshake synchronization. Use Value: Enables deterministic bus ownership handover via stored-data mode, reducing arbitration latency by eliminating external latch components. | Use Scenario: Managing concurrent access to a shared ISA-like expansion bus among multiple peripheral cards in retro-computing restoration projects. IC Role / Device Role / Timing Role: Inverting 3-state transceiver with dual registers acting as programmable bus buffer and temporary data staging point during DMA cycles. Use Value: 48 mA drive strength ensures reliable signal integrity across long backplane traces without added line drivers. |
| Military Avionics Data Multiplexing | Test Equipment Signal Routing |
Use Scenario: Multiplexing sensor telemetry and control commands across redundant MIL-STD-1553B auxiliary buses in legacy avionics subsystems. IC Role / Device Role / Timing Role: Bidirectional bus register managing time-critical data flow between processor and remote terminal interfaces with real-time bypass capability. Use Value: Select-control glitch immunity prevents spurious command injection during mode transitions - critical for flight-critical data paths. | Use Scenario: Configurable signal routing in automated test equipment (ATE) where stimulus/response paths must be dynamically reconfigured per test sequence. IC Role / Device Role / Timing Role: Programmable octal transceiver enabling hardware-selectable signal paths between DUT pins and measurement instruments via stored register states. Use Value: Independent OEAB/OEBA control allows per-bus isolation, supporting multi-stage parallel testing without software intervention. |
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-1NT | True (non-inverting) data path on both buses; identical pinout, timing, and drive specs | Required where signal polarity preservation is mandatory (e.g., direct connection to non-inverting bus controllers) | Select when system logic requires unmodified data polarity - no PCB changes needed |
| SN74AS651NT | Faster propagation (≤18 ns vs. ≤32 ns), higher IOL (48 mA), but AS family consumes more power and has stricter VIH/VIL thresholds | Suitable for high-speed upgrades where timing margin is constrained but power budget allows | Choose for performance-critical paths needing sub-20 ns delays; verify thermal design due to higher ICC |
Compared with SN74ALS652A-1NT and SN74AS651NT, the SN74ALS651A-1NT provides inverting logic essential for level-shifting or complement-based bus protocols, lower static power than AS variants, and proven reliability in long-lifecycle industrial deployments - making it optimal for cost-sensitive, stability-focused legacy system maintenance.
Availability
SN74ALS651A-1NT is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy computer bus arbitration, and military avionics data multiplexing requiring stable component supply across extended production lifecycles.
Supply support for SN74ALS651A-1NT 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The SN74ALS651A-1NT belongs to TI's legacy ALS logic product line, engineered for robust 5-V TTL system integration with enhanced noise immunity and drive capability - targeting long-life infrastructure and retro-design applications.
FAQ
What logic family does the SN74ALS651A-1NT belong to, and how does it differ from standard TTL?
The SN74ALS651A-1NT is an Advanced Low-Power Schottky (ALS) device, offering lower power consumption and higher speed than standard TTL while maintaining full voltage-level compatibility. It draws only ~52–82 mA ICC (vs. >100 mA for standard TTL), achieves 40 MHz operation, and features tighter VIH/VIL thresholds (2.0 V / 0.8 V). Its -1 version further increases IOL to 48 mA - a key differentiator for driving legacy bus loads. This makes SN74ALS651A-1NT ideal for upgrading aging TTL systems without redesigning logic levels or supply rails.
Does the SN74ALS651A-1NT support both real-time and stored data transfer modes, and how is mode selection implemented?
Yes, the SN74ALS651A-1NT supports both real-time and stored data transfer via dedicated select-control inputs SAB (for A→B path) and SBA (for B→A path). A low level on SAB or SBA selects real-time transfer (data passes directly through transceivers), while a high level selects stored data (output reflects contents of internal D-type flip-flops). Critically, the internal select-control circuitry eliminates decoding glitches during mode transitions - a feature confirmed in the SDAS066G datasheet Figure 1 and functional tables. This behavior is intrinsic to SN74ALS651A-1NT and requires no external logic.
What is the significance of the "-1" suffix in SN74ALS651A-1NT, and does it affect pin compatibility?
The "-1" suffix in SN74ALS651A-1NT denotes an enhanced-output version with increased low-level output current (IOL) specification: 48 mA (at VCC = 4.75–5.25 V), versus 24 mA for the standard SN74ALS651A. All other electrical, timing, and functional characteristics - including pinout, package (NT), and logic behavior - are identical. Therefore, SN74ALS651A-1NT is a drop-in replacement for SN74ALS651A in applications requiring higher drive strength, with no PCB or firmware changes needed. This is explicitly stated in the SDAS066G datasheet revision note.
Can the SN74ALS651A-1NT operate with mixed-voltage systems, such as interfacing 3.3-V controllers with 5-V buses?
No, the SN74ALS651A-1NT is a 5-V-only device with absolute maximum ratings specifying VCC = –0.5 V to 7 V and I/O voltage limits of –0.5 V to 5.5 V. Its input thresholds (VIH = 2.0 V, VIL = 0.8 V) and output swing (VOH ≥ 2.4 V, VOL ≤ 0.5 V) are defined for 5-V operation. Direct connection to 3.3-V logic risks overvoltage damage to the 3.3-V device and violates SN74ALS651A-1NT's input voltage spec. Level-shifting circuitry (e.g., TI SN74AVC series translators) is required for safe 3.3-V ↔ 5-V interfacing - a constraint confirmed across all recommended operating conditions tables in SDAS066G.
How does the SN74ALS651A-1NT handle bus contention during mode switching, and what design features prevent glitches?
The SN74ALS651A-1NT prevents bus contention and glitches during mode switching via two integrated design features: (1) its select-control logic (SAB/SBA) uses internal synchronization to eliminate race conditions during real-time ↔ stored transitions, and (2) output-enable inputs OEAB and OEBA allow precise, independent control of A- and B-bus drivers. As documented in SDAS066G Figure 1 and functional tables, setting OEAB = OEBA = H places both buses in high-impedance state during mode reconfiguration - isolating them from contention. This behavior is inherent to SN74ALS651A-1NT's architecture and requires no external timing control.
SN74ALS651A-1NT Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- -
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- -
- Number of Bits per Element:
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- Input Type:
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- Output Type:
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- Current - Output High, Low:
- -
- Voltage - Supply:
- -
- Operating Temperature:
- -
- Grade:
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SN74ALS651A-1NT FAQ
1.How can I place an order for SN74ALS651A-1NT through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS651A-1NT 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-1NT reliable?
The price and inventory of SN74ALS651A-1NT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS651A-1NT is usually 5 days.
3.What payment methods are accepted for SN74ALS651A-1NT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS651A-1NT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS651A-1NT?
SN74ALS651A-1NT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS651A-1NT 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-1NT?
For technical support, including SN74ALS651A-1NT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS651A-1NT requirements.
6.How does Aetrix verify that SN74ALS651A-1NT is sourced from the original manufacturer or authorized distributors?
All SN74ALS651A-1NT 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-1NT meets industry standards.
7.What is the process for return or replacement of SN74ALS651A-1NT?
All SN74ALS651A-1NT units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS651A-1NT, 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-1NT part is unused and in its original packaging.
Return procedure for SN74ALS651A-1NT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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