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Texas Instruments SN74ALS646A-1NT
- Part No.:
- SN74ALS646A-1NT
- Manufacturer:
- Texas Instruments
- Package:
- 24-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74ALS646A-1NT.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24DIP
- Quantity:
- Payment:
- Shipping:
Inventory:3,644
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Product details
Overview
SN74ALS646A-1NT from Texas Instruments is an octal bus transceiver and register IC with 3-state outputs, designed for bidirectional data flow between A and B buses in TTL-compatible systems. It features independent A/B registers, real-time or stored data multiplexing via SAB/SBA controls, true (non-inverting) logic path, and supports clocked storage on CLKAB/CLKBA rising edges. It operates from 0°C to 70°C with 5 V supply and delivers 48 mA low-level output drive in the -1 version - ideal for legacy industrial backplane and memory interface applications.
For engineers reviewing the SN74ALS646A-1NT datasheet, SN74ALS646A-1NT pinout, SN74ALS646A-1NT application, or SN74ALS646A-1NT equivalent, this device is selected for synchronous bus isolation, dual-bus register staging, and glitch-free multiplexed data routing where timing-critical 3-state control and register retention are required.
Technical Context
The SN74ALS646A-1NT integrates eight D-type flip-flops (four per bus), dual-clock edge-triggered storage (CLKAB for A→register, CLKBA for B→register), and direction-controlled 3-state transceivers. Its select-control logic (SAB/SBA) eliminates decoding glitches during transitions between transparent and stored data modes.
It supports four core bus-management functions: real-time A↔B transfer, isolated A/B register storage, and selective output of stored data to either bus - all governed by OE (output enable), DIR (direction), and clock/enable timing relationships defined in its function table.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | Advanced Low-Power Schottky (ALS) TTL - ensures compatibility with legacy 5 V TTL systems and lower power vs standard LS. |
| Bus Width | Octal (8-bit) bidirectional - enables full parallel data transfer between two 8-bit buses (A1–A8 and B1–B8). |
| Output Type | 3-state non-inverting - allows shared bus operation with high-impedance disable; no open-collector mode. |
| Max Clock Frequency | 40 MHz - supports high-speed synchronous register loading (CLKAB/CLKBA rising edge) in real-time bus applications. |
| IOL (–1 version) | 48 mA - enhanced sink capability enables direct driving of multiple TTL inputs or moderate capacitive loads without buffers. |
| Operating Temperature | 0°C to 70°C - commercial-grade rating suitable for industrial control panels and embedded computing chassis. |
| Supply Voltage | 4.5 V to 5.5 V - tight regulation tolerance ensures stable operation across noisy 5 V rails common in legacy PCBs. |
Pinout & Package
SN74ALS646A-1NT uses a 24-pin plastic DIP (Dual In-line Package) with 300-mil width, designated NT package per TI documentation. Pin numbering follows standard DIP convention (pin 1 at top-left corner, counterclockwise).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | CLKAB | Rising-edge clock input for latching data from A bus into internal A register. |
| 2 | SAB | Select control: determines whether A-bus data output is real-time (transparent) or stored. |
| 3 | DIR | Direction control: when OE = L, sets data flow direction (L = B→A, H = A→B). |
| 4–11 | A1–A8 | 8-bit bidirectional I/O port for A-side bus interface; inputs when receiving, outputs when driving. |
| 12 | GND | Ground reference for all internal logic and I/O circuits. |
| 13–20 | B1–B8 | 8-bit bidirectional I/O port for B-side bus interface; functionally symmetric to A ports. |
| 21 | OE | Active-low output enable: disables all 3-state outputs (A/B) when high; enables transceiver/register output when low. |
| 22 | SBA | Select control: determines whether B-bus data output is real-time or stored. |
| 23 | CLKBA | Rising-edge clock input for latching data from B bus into internal B register. |
| 24 | VCC | +5 V power supply input; decoupling capacitor required near pin for noise immunity. |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B Registers | Enables simultaneous capture and retention of data from both buses - critical for handshake protocols and pipeline staging. |
| Glitch-Free Multiplexing | SAB/SBA control logic prevents output glitches during transitions between real-time and stored data modes - improves signal integrity in timing-sensitive systems. |
| True (Non-Inverting) Data Path | Preserves logic polarity end-to-end - simplifies system-level timing analysis and avoids inversion-related setup/hold complications. |
| 48 mA IOL (–1 version) | Supports fan-out of ≥20 standard TTL loads - reduces need for external buffer stages in dense backplane designs. |
| Real-Time + Stored Mode Flexibility | Allows dynamic selection of live bus data or previously latched values - essential for diagnostic readback, shadow register access, and fault-tolerant arbitration. |
Applications
| Industrial Backplane Interface | Legacy Memory Subsystem Control |
|---|---|
|
Use Scenario: Isolating CPU address/data buses from peripheral expansion slots in programmable logic controllers (PLCs). IC Role / Device Role / Timing Role: Bidirectional bus transceiver with register staging to synchronize asynchronous peripheral responses and prevent bus contention. Use Value: Enables deterministic timing via CLKAB/CLKBA-synchronized register capture and glitch-free SAB/SBA switching - critical for deterministic scan-cycle execution. |
Use Scenario: Managing data flow between microprocessor and dual-port SRAM or ROM in retro-computing hardware. IC Role / Device Role / Timing Role: Octal register-based transceiver providing temporary storage during memory read-modify-write cycles. Use Value: Eliminates need for external latch ICs by integrating storage and 3-state control - reduces component count and board area in space-constrained designs. |
| Test Equipment Bus Arbitration | Automated Test System (ATE) Signal Routing |
|
Use Scenario: Arbitrating shared test bus access among multiple instrument modules in rack-mounted ATE mainframes. IC Role / Device Role / Timing Role: Direction-controlled transceiver with independent A/B registers for buffering and time-aligned signal injection. Use Value: DIR and OE allow precise control over bus ownership; 40 MHz max clock supports high-throughput stimulus/response sequencing. |
Use Scenario: Routing digital stimulus signals from pattern generators to DUT pins while capturing response data in real time. IC Role / Device Role / Timing Role: Dual-bus register staging element enabling simultaneous capture (on CLKBA) and output (via SBA) without bus conflict. Use Value: Real-time + stored mode operation permits concurrent acquisition and playback - increasing test throughput in multi-site parallel testing. |
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 |
|---|---|---|---|
| SN74ALS648A-1NT | Inverting data path (vs. true logic in SN74ALS646A-1NT); identical pinout, timing, and electrical specs otherwise. | Required where system-level logic inversion is acceptable or needed to match downstream gate polarity. | Select SN74ALS648A-1NT only if inverting behavior aligns with overall signal chain polarity budget - not a drop-in replacement without logic review. |
| SN74AS646DW | Faster propagation delays (e.g., tPHL ≤ 9 ns vs. ≤ 17 ns), higher ICC (120–195 mA), and 90 MHz fmax - but no -1 IOL enhancement; SOIC-24 package. | Better suited for high-speed digital test equipment or FPGA interconnect where speed outweighs power and package constraints. | Choose SN74AS646DW for new designs requiring >40 MHz operation; SN74ALS646A-1NT remains optimal for cost-sensitive, power-constrained, or DIP-restricted legacy upgrades. |
Compared with SN74ALS648A-1NT and SN74AS646DW, the SN74ALS646A-1NT uniquely balances 48 mA drive strength, DIP packaging, and true logic polarity - making it the preferred choice for maintaining signal integrity and minimizing redesign effort in existing industrial backplane systems.
Availability
SN74ALS646A-1NT is available at Aetrix Electronics and suitable for industrial automation, legacy test equipment, and retro-computing hardware requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74ALS646A-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 global semiconductor leader founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The SN74ALS646A belongs to TI's legacy ALS logic family - engineered for reliable 5 V TTL interoperability, low power consumption, and robust noise immunity in mission-critical industrial control environments.
FAQ
What is the key functional difference between SN74ALS646A-1NT and standard SN74ALS646A?
The SN74ALS646A-1NT is the "-1" variant, distinguished by its enhanced low-level output current rating of 48 mA (vs. 24 mA for the standard version) under specified VCC conditions (4.75 V to 5.25 V). This allows stronger drive capability for heavier TTL fan-out or capacitive loads without external buffers - a critical advantage in legacy backplane and industrial I/O designs where signal integrity margins are tight. All other logic, timing, and pinout characteristics remain identical to SN74ALS646A.
Does SN74ALS646A-1NT support both real-time and stored data modes simultaneously?
Yes. The SN74ALS646A-1NT supports concurrent real-time and stored data operation via independent SAB (for A-bus) and SBA (for B-bus) controls. For example, SAB = L selects real-time A→B transfer while SBA = H selects stored B→A output - enabling asymmetric data routing. This capability is implemented in hardware with glitch-free logic, allowing seamless transitions without bus contention or metastability, as verified in TI's SDAS039F function tables and timing diagrams.
Can SN74ALS646A-1NT be used in place of SN74ALS648A-1NT?
No - SN74ALS646A-1NT and SN74ALS648A-1NT are not functionally interchangeable due to fundamental logic polarity differences: SN74ALS646A-1NT provides a true (non-inverting) data path, while SN74ALS648A-1NT is inverting. Swapping them without adjusting upstream/downstream logic will invert all 8-bit data - causing system failure. They share identical pinout, timing, and electrical specs, but polarity must be validated at the system level before substitution.
What is the maximum clock frequency supported by SN74ALS646A-1NT for register loading?
The SN74ALS646A-1NT supports a maximum clock frequency of 40 MHz for reliable register loading on CLKAB and CLKBA rising edges, as specified in TI's recommended operating conditions (SDAS039F, p.6). This rating assumes VCC = 4.5 V to 5.5 V, CL = 50 pF, and TA = 0°C to 70°C. At 40 MHz, minimum pulse width is 12.5 ns (tw), and setup/hold times are 10 ns/0 ns respectively - design margins must accommodate these values in PCB layout and clock distribution.
Is SN74ALS646A-1NT RoHS compliant?
No. The SN74ALS646A-1NT uses a plastic DIP (NT) package with leaded solder finish and is not RoHS compliant. TI's packaging addendum confirms "No" for RoHS status and "SNPB" (tin-lead) for lead finish. It is intended for legacy repair, military/aerospace (where exemptions apply), or industrial applications exempt from RoHS directives. For RoHS-compliant alternatives, consider SOIC-packaged variants like SN74ALS646ADWR (NIPDAU finish, Level-1 MSL).
SN74ALS646A-1NT 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
SN74ALS646A-1NT FAQ
1.How can I place an order for SN74ALS646A-1NT through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS646A-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 SN74ALS646A-1NT reliable?
The price and inventory of SN74ALS646A-1NT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS646A-1NT is usually 5 days.
3.What payment methods are accepted for SN74ALS646A-1NT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS646A-1NT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS646A-1NT?
SN74ALS646A-1NT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS646A-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 SN74ALS646A-1NT?
For technical support, including SN74ALS646A-1NT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS646A-1NT requirements.
6.How does Aetrix verify that SN74ALS646A-1NT is sourced from the original manufacturer or authorized distributors?
All SN74ALS646A-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 SN74ALS646A-1NT meets industry standards.
7.What is the process for return or replacement of SN74ALS646A-1NT?
All SN74ALS646A-1NT units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS646A-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 SN74ALS646A-1NT part is unused and in its original packaging.
Return procedure for SN74ALS646A-1NT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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