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Texas Instruments SN74ALS646ANT
- Part No.:
- SN74ALS646ANT
- Manufacturer:
- Texas Instruments
- Package:
- 24-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74ALS646ANT.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24DIP
- Quantity:
- Payment:
- Shipping:
Inventory:4,546
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Product details
Overview
SN74ALS646ANT 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 directionality, and OE-gated 3-state output enable. It operates at up to 40 MHz clock frequency with 5 V supply and supports industrial temperature range (0°C to 70°C), commonly used in legacy backplane interfaces and buffered address/data bus isolation.
For engineers reviewing the SN74ALS646ANT datasheet, SN74ALS646ANT pinout, SN74ALS646ANT application, or SN74ALS646ANT equivalent, key selection criteria include its dual-register storage capability, glitch-free select control, true (non-inverting) data path, 24-pin PDIP (NT) package, and compatibility with ALS logic family timing and drive strength.
Technical Context
The SN74ALS646ANT integrates eight identical bidirectional channels, each with D-type flip-flops for A- and B-bus data latching on CLKAB↑ or CLKBA↑ transitions. Its control architecture separates bus direction (DIR), output enable (OE), and data source selection (SAB/SBA), enabling four distinct bus-management modes: real-time A→B, B→A, simultaneous A/B storage, and stored-data transfer to either bus.
It implements a synchronous, edge-triggered register interface with asynchronous 3-state output control. The select logic eliminates decoding glitches during transitions between transparent and stored data paths, and input functions remain active even when outputs are disabled - allowing concurrent storage and transmission.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | Advanced Low-Power Schottky (ALS), TTL-compatible voltage thresholds (VIH = 2 V, VIL = 0.8 V) |
| Max Clock Frequency | 40 MHz - enables high-speed bus arbitration in legacy computing and instrumentation systems |
| Output Drive | IOL = 24 mA (standard), 48 mA (-1 version); IOH = –15 mA - sufficient to drive multiple TTL loads without buffers |
| Propagation Delay | tPLH/tPHL ≤ 30 ns (A↔B), ≤ 35 ns (CLK→bus) - ensures timing margin in 25 ns–40 ns system clocks |
| Operating Temperature | 0°C to 70°C - qualified for commercial/industrial equipment, not military-grade |
| Supply Voltage | VCC = 4.5 V to 5.5 V - robust against nominal 5 V rail variation in aging power supplies |
| Package | 24-pin plastic DIP (NT), 300-mil width - compatible with through-hole prototyping and legacy PCBs |
Pinout & Package
SN74ALS646ANT is housed in a 24-pin plastic dual in-line package (PDIP, NT package), 300-mil width, with standard through-hole mounting and 0.1-inch pin pitch.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | CLKAB | Clock input for latching data from A bus into B-register on rising edge |
| 2 | SAB | Select control: low = real-time A→B transfer; high = stored A→B transfer |
| 3 | DIR | Direction control: low = B→A; high = A→B (active when OE = low) |
| 4–11 | A1–A8 | 8-bit data inputs/outputs for A-side bus (bidirectional I/O with 3-state) |
| 12 | GND | Ground reference for all logic and I/O circuits |
| 13–20 | B1–B8 | 8-bit data inputs/outputs for B-side bus (bidirectional I/O with 3-state) |
| 21 | OE | Output enable: low = enabled; high = 3-state (high-impedance) outputs |
| 22 | SBA | Select control: low = real-time B→A transfer; high = stored B→A transfer |
| 23 | CLKBA | Clock input for latching data from B bus into A-register on rising edge |
| 24 | VCC | +5 V power supply input (4.5 V–5.5 V operating range) |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B Registers | Enables simultaneous capture and retention of data from both buses, supporting time-multiplexed bus sharing |
| Glitch-Free Select Logic | SAB/SBA control eliminates transient glitches during switching between real-time and stored data paths |
| True (Non-Inverting) Data Path | Maintains signal polarity across transceiver operation - critical for address/data integrity in bus architectures |
| Asynchronous Input Enable | Data inputs remain functional even when outputs are 3-stated (OE high), enabling concurrent storage and bus arbitration |
| Multiple Package Options | Available in PDIP (NT), SOIC (DW), and ceramic DIP (JT) - supports legacy repair, prototyping, and high-reliability designs |
Applications
| Backplane Bus Isolation | Microprocessor Address/Data Buffering |
|---|---|
|
Use Scenario: Isolating CPU and peripheral buses in modular rack-mounted instrumentation systems to prevent signal contention and ground loops. IC Role / Device Role / Timing Role: Bidirectional 3-state transceiver with register hold, synchronizing data transfers between mismatched clock domains using CLKAB/CLKBA. Use Value: Prevents bus collisions during hot-swap or reconfiguration while retaining last valid state via internal registers. |
Use Scenario: Buffering 8-bit address or data lines between Z80 or 8085 microprocessors and memory/peripheral chips on single-board computers. IC Role / Device Role / Timing Role: Octal register-transceiver providing latch + direction control + 3-state enable for shared bus access. Use Value: Eliminates need for separate latches and transceivers, reducing component count and board space in cost-sensitive designs. |
| Legacy Industrial Controller I/O Expansion | Dual-Bus Multiplexing in Test Equipment |
|
Use Scenario: Expanding I/O capacity in programmable logic controllers (PLCs) by interfacing local I/O modules with main controller bus. IC Role / Device Role / Timing Role: Register-based transceiver storing sensor/actuator data during bus arbitration cycles, then releasing on command. Use Value: Enables deterministic response timing and jitter-free data handoff in real-time control loops. |
Use Scenario: Switching between stimulus and measurement buses in automated test equipment (ATE) for sequential device characterization. IC Role / Device Role / Timing Role: Multiplexed transceiver selecting between live DUT signals (real-time) and pre-loaded test vectors (stored). Use Value: Reduces test setup latency and eliminates external multiplexer timing skew in high-precision analog/digital validation. |
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 |
|---|---|---|---|
| SN74ALS646ADW | Same functionality and timing, but in 24-pin SOIC (DW) package; RoHS-compliant NiPdAu finish; MSL Level-1 | Designed for surface-mount production; unsuitable for through-hole sockets or manual prototyping | Select when migrating to SMT assembly or requiring modern compliance; verify PCB footprint and thermal profile. |
| SN74AS646DW | Faster propagation (≤9 ns vs. ≤30 ns), higher drive (IOL = 48 mA), AS logic family - requires tighter layout and decoupling | Targeted at high-speed systems (>50 MHz); incompatible with ALS-level noise margins and input thresholds | Choose only if speed is critical and full AS-family system integration is feasible; not a drop-in replacement. |
Compared with SN74ALS646ADW and SN74AS646DW, the SN74ALS646ANT offers proven reliability in legacy through-hole systems, relaxed timing margins for easier layout, and direct socket compatibility - making it optimal for repair, maintenance, and low-volume industrial upgrades where soldering constraints or obsolescence risk exist.
Availability
SN74ALS646ANT is available at Aetrix Electronics and suitable for backplane bus isolation, microprocessor address/data buffering, and legacy industrial controller I/O expansion requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS646ANT 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 with broad industrial, automotive, and communications reach.
The SN74ALS646ANT belongs to TI's legacy TTL-compatible logic portfolio, engineered specifically for robust, low-power bus interfacing in industrial control, test equipment, and retrocomputing systems where reliability and pin compatibility are paramount.
FAQ
What is the maximum clock frequency supported by the SN74ALS646ANT?
The SN74ALS646ANT supports a maximum clock frequency of 40 MHz under recommended operating conditions (VCC = 4.5 V to 5.5 V, TA = 0°C to 70°C). This rating applies to both CLKAB and CLKBA inputs and ensures reliable register capture of A- or B-bus data on each rising edge. Timing margins must account for tSU = 10 ns and tH = 0 ns per datasheet SDAS039F.
Does the SN74ALS646ANT support inverting data paths?
No, the SN74ALS646ANT provides a true (non-inverting) data path. It is functionally distinct from the SN74ALS648A, which offers inverting logic. The SN74ALS646ANT preserves signal polarity across all transceiver and register operations - essential for address bus integrity and deterministic control signaling in synchronous systems.
Can the SN74ALS646ANT operate with a 3.3 V supply?
No, the SN74ALS646ANT is an ALS-family TTL device requiring a 4.5 V to 5.5 V supply. Operation below 4.5 V violates recommended conditions and risks incorrect logic thresholds, reduced noise margin, and failure to meet timing specs. For 3.3 V systems, consider level-shifting circuitry or modern 3.3 V-compatible transceivers like the SN74LVC245A.
What does "NT" signify in the SN74ALS646ANT part number?
The "NT" suffix in SN74ALS646ANT denotes the plastic dual in-line package (PDIP) variant - specifically a 24-pin, 300-mil wide, through-hole package with industry-standard pinout and mechanical dimensions. This distinguishes it from DW (SOIC) and JT (ceramic DIP) variants, and confirms compatibility with legacy sockets and wave-solder processes.
How does the SN74ALS646ANT handle simultaneous read/write operations on A and B buses?
The SN74ALS646ANT supports independent A- and B-bus storage: data on either bus can be latched into its respective register on CLKAB↑ or CLKBA↑, regardless of OE or DIR state. While only one bus may drive outputs at a time (per DIR/OE), both registers retain their values - enabling true dual-bus snapshot capability for arbitration, diagnostics, or fault logging without external memory.
SN74ALS646ANT Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 24-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- 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:
- Through Hole
- Supplier Device Package:
- 24-PDIP
SN74ALS646ANT FAQ
1.How can I place an order for SN74ALS646ANT through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS646ANT 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 SN74ALS646ANT reliable?
The price and inventory of SN74ALS646ANT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS646ANT is usually 5 days.
3.What payment methods are accepted for SN74ALS646ANT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS646ANT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS646ANT?
SN74ALS646ANT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS646ANT 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 SN74ALS646ANT?
For technical support, including SN74ALS646ANT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS646ANT requirements.
6.How does Aetrix verify that SN74ALS646ANT is sourced from the original manufacturer or authorized distributors?
All SN74ALS646ANT 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 SN74ALS646ANT meets industry standards.
7.What is the process for return or replacement of SN74ALS646ANT?
All SN74ALS646ANT units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS646ANT, 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 SN74ALS646ANT part is unused and in its original packaging.
Return procedure for SN74ALS646ANT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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