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Texas Instruments SN74AS648NT
- Part No.:
- SN74AS648NT
- Manufacturer:
- Texas Instruments
- Package:
- 24-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74AS648NT.pdf
- Description:
- IC TRANSCEIVER INVERT 5.5V 24DIP
- Quantity:
- Payment:
- Shipping:
Inventory:3,534
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Product details
Overview
SN74AS648NT from Texas Instruments is an octal bus transceiver and register with 3-state outputs, designed for bidirectional data flow control between two 8-bit buses (A and B) in TTL-compatible systems. It features independent A/B registers, true/inverting data paths (this variant is inverting), clocked storage (CLKAB/CLKBA), select-control (SAB/SBA), direction (DIR), and output-enable (OE) logic - enabling real-time or stored data transfer in industrial control backplanes and legacy computing interfaces.
For engineers reviewing the SN74AS648NT datasheet, SN74AS648NT pinout, SN74AS648NT application, or SN74AS648NT equivalent, key selection criteria include its 90 MHz max clock frequency, 48 mA low-level output drive, inverting data path, 24-pin plastic DIP (NT) package, and operation over 0°C to 70°C - critical for bus arbitration, buffered memory expansion, and synchronous data multiplexing in aging but mission-critical embedded systems.
Technical Context
The SN74AS648NT implements dual 8-bit D-type flip-flop registers (A and B sides) with asynchronous 3-state output control. Its architecture supports four bus-management modes: real-time A→B or B→A transfer, simultaneous A/B storage, and selective output of stored data - all governed by OE, DIR, SAB, SBA, CLKAB, and CLKBA inputs.
Unlike simpler transceivers, it eliminates multiplexer decoding glitches during stored/real-time transitions via dedicated select-control circuitry. The inverting output logic (per SN74AS648 family specification) applies to all eight B→A and A→B data paths when enabled, while input functions remain always active for concurrent capture on clock edges.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | Advanced Schottky TTL (AS) - ensures high-speed operation with low power-delay product vs. standard TTL. |
| Max Clock Frequency | 90 MHz - enables high-throughput synchronous bus interfacing in fast legacy systems. |
| IOL (Low-Level Output) | 48 mA - drives heavy capacitive loads or multiple TTL inputs without external buffers. |
| Propagation Delay (tPHL/tPLH) | 1–9 ns - guarantees tight timing margins for 90 MHz clock domains and sub-10 ns setup/hold compliance. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade industrial and computing equipment environments. |
| Supply Voltage Range | 4.5 V to 5.5 V - compatible with standard 5 V regulated rails; absolute max 7 V prevents latch-up under transient conditions. |
| Data Path Logic | Inverting - output complements input on both A→B and B→A transfers, required for specific bus inversion protocols. |
Pinout & Package
SN74AS648NT uses a 24-pin plastic dual in-line package (DIP), 300-mil width, with through-hole mounting. Pin numbering follows standard DIP convention (pin 1 at top-left corner, counterclockwise).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | CLKAB | Clocks data from bus A into A-register on rising edge; controls A→B stored-data transfer timing. |
| 2 | SAB | Selects A-register output to bus B (when DIR=H, OE=L); enables stored-data mode. |
| 3 | DIR | Direction control: H = A→B transfer, L = B→A transfer; determines active data path. |
| 4–11 | A1–A8 | 8-bit bidirectional data port A; inputs when capturing, outputs when enabled and selected. |
| 12 | GND | Ground reference for all logic and I/O; must be low-impedance for noise immunity. |
| 13–20 | B1–B8 | 8-bit bidirectional data port B; symmetric role to A ports with inverted output logic. |
| 21 | OE | Output enable: L = enable outputs, H = 3-state (high-impedance) - isolates bus drivers. |
| 22 | SBA | Selects B-register output to bus A (when DIR=L, OE=L); enables stored-data mode. |
| 23 | CLKBA | Clocks data from bus B into B-register on rising edge; controls B→A stored-data transfer timing. |
| 24 | VCC | +5 V supply; decoupling capacitor required near pin for stable high-speed switching. |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B Registers | Enables concurrent capture of data from both buses on separate clock edges - essential for ping-pong buffering and dual-bus synchronization. |
| Glitch-Free Select Control | Eliminates transient shorts during stored/real-time mode switching - prevents bus contention in time-critical arbitration. |
| Inverting Data Path | Provides hardware-level data complementation without external inverters - reduces component count in parity or checksum circuits. |
| Always-Enabled Inputs | Input functions remain active even when outputs are disabled (OE=H), allowing continuous register updates during bus isolation. |
| High-Drive 3-State Outputs | 48 mA sink capability supports direct driving of up to 20 standard TTL loads - eliminates need for line drivers in dense backplane designs. |
Applications
| Industrial Backplane Interface | Legacy Memory Expansion |
|---|---|
Use Scenario: Interfacing a microprocessor bus to multiple peripheral cards in a ruggedized PLC rack with shared address/data lines. IC Role / Device Role / Timing Role: SN74AS648NT acts as a registered, direction-controlled bus transceiver - latching address/data on CLKAB/CLKBA edges and selectively routing stored or live signals to prevent contention. Use Value: Its 90 MHz clock tolerance and 48 mA drive ensure reliable signal integrity across long backplane traces, while inverting logic matches legacy memory controller expectations. | Use Scenario: Adding external RAM or ROM to an 8-bit microcontroller system where bus loading exceeds native driver capability. IC Role / Device Role / Timing Role: SN74AS648NT serves as a registered buffer between MCU data/address bus and memory device - storing control signals and gating memory access via OE/DIR. Use Value: Independent A/B registers allow prefetching of next memory word during current cycle, improving effective throughput without CPU intervention. |
| Test Equipment Bus Arbitration | Synchronous Data Multiplexer |
Use Scenario: Managing shared GPIB or IEEE-488 bus access among multiple instruments in automated test systems. IC Role / Device Role / Timing Role: SN74AS648NT functions as a programmable bus switch with storage - holding instrument responses in registers and releasing them synchronously upon master request. Use Value: Glitch-free SAB/SBA control prevents spurious bus signals during arbitration handoff, ensuring protocol compliance and measurement repeatability. | Use Scenario: Routing sensor data streams from multiple analog front-ends to a single ADC or DSP in real-time monitoring systems. IC Role / Device Role / Timing Role: SN74AS648NT operates as a clock-synchronized multiplexer - sampling parallel sensor outputs on CLKAB, then serially presenting them via DIR/OE sequencing. Use Value: Inverting output logic aligns with differential signaling requirements of certain ADC interfaces, reducing external level-shifting components. |
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 | ALS family: lower speed (40 MHz max), lower drive (24 mA IOL), non-inverting output logic. | Suitable for lower-power, lower-frequency systems where propagation delay and drive strength are less critical. | Choose SN74ALS648A only if 90 MHz operation and 48 mA drive are unnecessary - avoids over-spec'ing cost and power. |
| SN74AS646 | Same AS family, same speed/drive, but true (non-inverting) data path instead of inverting. | Required where bus protocol mandates non-inverted data transfer - e.g., direct replacement in non-inverting memory subsystems. | Select SN74AS646 only when inverting logic would break existing data integrity checks or handshake sequences. |
Compared with SN74ALS648A and SN74AS646, the SN74AS648NT delivers superior timing performance and higher drive strength while maintaining pin compatibility and identical register/control architecture - making it the optimal choice for upgrading legacy AS/ALS-based systems requiring faster, more robust bus interfacing.
Availability
SN74AS648NT is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy memory expansion, test equipment bus arbitration, and synchronous data multiplexing requiring stable component supply and long-term obsolescence management.
Supply support for SN74AS648NT 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 SN74AS648NT belongs to TI's legacy TTL logic portfolio, engineered specifically for high-reliability, high-speed bus interfacing in commercial-grade computing and control systems - emphasizing timing precision, noise immunity, and backward compatibility.
FAQ
What is the maximum operating clock frequency supported by the SN74AS648NT?
The SN74AS648NT supports a maximum clock frequency of 90 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 is validated per TI's characterization data for the SN74AS648 family. The SN74AS648NT achieves this speed due to its Advanced Schottky TTL process, which minimizes propagation delay while maintaining noise margin - critical for high-throughput bus synchronization in legacy systems.
Does the SN74AS648NT provide inverting or non-inverting data transfer between buses?
The SN74AS648NT provides inverting data transfer on both A→B and B→A paths when outputs are enabled. This behavior is defined in the device family documentation (SDAS039F) and distinguishes it from the SN74AS646 variant, which offers true (non-inverting) logic. The inversion occurs at the output stage and applies regardless of DIR setting or register selection - a fixed architectural feature of the SN74AS648NT that must be accounted for in system-level signal interpretation.
What package type and pin count does the SN74AS648NT use?
The SN74AS648NT uses a 24-pin plastic dual in-line package (DIP), designated "NT" by Texas Instruments, with 300-mil body width and through-hole mounting. Pin 1 is located at the top-left corner (notch side), and the package conforms to JEDEC MS-001 standards. This package is distinct from the SOIC (DW) and ceramic DIP (JT) variants - the NT version is optimized for prototyping, repair, and legacy board assemblies requiring socketed components.
How does the SN74AS648NT handle bus contention during mode transitions?
The SN74AS648NT eliminates bus contention during stored/real-time mode transitions using dedicated glitch-free select-control circuitry for SAB and SBA inputs. Unlike discrete gate-based multiplexers, its internal logic ensures no intermediate short-circuit state occurs when switching between real-time and registered data paths - verified by TI's functional timing diagrams and test waveforms. This design prevents momentary bus shorts that could corrupt data or damage drivers in multi-drop configurations.
Can the SN74AS648NT operate with a 3.3 V supply voltage?
No, the SN74AS648NT is not rated for 3.3 V operation. Its recommended supply voltage range is strictly 4.5 V to 5.5 V, with absolute maximum VCC at 7 V. Operating below 4.5 V risks violating VIH/VIL thresholds, degrading noise margins, and causing metastability in register clocks. For 3.3 V systems, TI recommends level-shifting interfaces or newer logic families (e.g., LVC or AUP) - the SN74AS648NT requires a compliant 5 V rail to guarantee specified timing, drive strength, and logic levels.
SN74AS648NT Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AS
- Package/Case:
- 24-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Logic Type:
- Transceiver, Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- -
- Output Type:
- 3-State
- Current - Output High, Low:
- 15mA, 48mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 24-PDIP
SN74AS648NT FAQ
1.How can I place an order for SN74AS648NT through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS648NT 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 SN74AS648NT reliable?
The price and inventory of SN74AS648NT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS648NT is usually 5 days.
3.What payment methods are accepted for SN74AS648NT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS648NT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS648NT?
SN74AS648NT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS648NT 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 SN74AS648NT?
For technical support, including SN74AS648NT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS648NT requirements.
6.How does Aetrix verify that SN74AS648NT is sourced from the original manufacturer or authorized distributors?
All SN74AS648NT 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 SN74AS648NT meets industry standards.
7.What is the process for return or replacement of SN74AS648NT?
All SN74AS648NT units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS648NT, 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 SN74AS648NT part is unused and in its original packaging.
Return procedure for SN74AS648NT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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