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Texas Instruments SN74ALS648ADW
- Part No.:
- SN74ALS648ADW
- Manufacturer:
- Texas Instruments
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS648ADW.pdf
- Description:
- IC TXRX INVERT 5.5V 24SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,953
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Product details
Overview
SN74ALS648ADW from Texas Instruments is an octal bus transceiver and register IC with 3-state inverting outputs, designed for bidirectional data flow between A and B buses in legacy TTL-based systems. It features independent A/B registers, real-time or stored data multiplexing via SAB/SBA controls, DIR-controlled direction, OE-enabled 3-state output, and operates at up to 40 MHz clock frequency across 0°C to 70°C.
For engineers reviewing the SN74ALS648ADW datasheet, SN74ALS648ADW pinout, SN74ALS648ADW application, or SN74ALS648ADW equivalent, this device supports critical bus management functions including isolated storage, transparent transfer, and glitch-free multiplexing of 8-bit parallel data in industrial control backplanes, test equipment interfaces, and retro-computing memory expansion subsystems.
Technical Context
The SN74ALS648ADW integrates dual 8-bit D-type flip-flop registers (A-side and B-side), a bidirectional transceiver path with inverting logic, and asynchronous select-control circuitry that eliminates decoding glitches during transitions between real-time and stored data modes. Its CLKAB/CLKBA inputs latch data on low-to-high transitions, while DIR determines bus direction when OE is active low.
Control logic enables four distinct operational modes: real-time A→B or B→A transfer, simultaneous storage from either bus, and selective output of stored data to one or both buses - all without requiring external decode logic. The device maintains input functionality even when outputs are disabled, supporting concurrent data capture and conditional forwarding.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | Advanced Low-Power Schottky (ALS) TTL - ensures compatibility with legacy 5 V TTL systems while reducing power vs standard LS. |
| Bus Width | Octal (8-bit) - supports full byte-wide parallel data paths between two independent buses. |
| Output Type | Inverting 3-state - provides active-low output polarity and high-impedance disable for shared-bus arbitration. |
| Max Clock Frequency | 40 MHz - enables high-speed register loading in timing-critical bus interface applications. |
| Supply Voltage | 4.5 V to 5.5 V - operates within standard 5 V ±10% rail tolerances common in industrial and embedded platforms. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade environments including office automation and lab instrumentation. |
| Propagation Delay | tPLH/tPHL ≤ 33 ns (A↔B) - guarantees sub-35 ns data path latency for deterministic timing budgets. |
Pinout & Package
SN74ALS648ADW uses a 24-pin SOIC (DW) package with 300-mil width, surface-mount footprint, and RoHS-compliant NiPdAu lead finish. Pin 1 is located at the top-left corner adjacent to the index mark.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2, 4–11, 13, 14, 16–19, 22, 23 | A1–A8, B1–B8 I/O ports | Octal bidirectional data terminals - A-side and B-side pins support simultaneous input capture and output driving with inverting logic. |
| 3 | DIR | Direction control - low = B→A transfer, high = A→B transfer; defines active data flow path when OE is low. |
| 12, 20 | NC | No internal connection - must be left unconnected; no pull-up/down or routing required. |
| 15 | GND | Ground reference - primary return path for all logic and I/O currents; requires low-impedance PCB plane connection. |
| 24 | VCC | Positive supply - powers internal logic and output drivers; requires local 0.1 µF ceramic decoupling capacitor. |
| 21 | OE | Output enable - active low; disables all outputs to high-impedance state while preserving input functionality. |
| 1, 23 | CLKAB, CLKBA | Register clock inputs - low-to-high edge latches data from A bus (CLKAB) or B bus (CLKBA) into respective registers. |
| 2, 22 | SAB, SBA | Select controls - determine whether transceiver outputs deliver real-time or stored data; eliminate multiplexer glitches. |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B Registers | Enables concurrent storage of data from both buses - critical for handshake protocols and buffered interprocessor communication. |
| Glitch-Free Multiplexing | Hardware-select logic prevents transient invalid states during mode switching between real-time and stored data outputs. |
| Inverting Output Logic | Provides native signal inversion without external gates - simplifies design in systems requiring complemented bus signals. |
| Input-Enabled During Output Disable | Allows continuous data sampling on A/B ports even when OE disables outputs - essential for monitoring or diagnostic bus snooping. |
| SOIC-24 Package | Standardized 300-mil surface-mount footprint compatible with automated assembly and legacy board layouts. |
Applications
| Industrial Backplane Interface | Legacy Test Equipment Bus |
|---|---|
Use Scenario: Interfacing microcontroller-based I/O modules to a shared 8-bit data backplane in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional bus transceiver and register - isolates module address/data lines, stores command sequences, and forwards real-time sensor readings. Use Value: Eliminates need for discrete latches and direction logic, reducing component count and PCB area while ensuring deterministic 40 MHz timing compliance. | Use Scenario: Connecting digital pattern generators to DUT interfaces in automated test systems using TTL-level parallel buses. IC Role / Device Role / Timing Role: Octal register-transceiver - captures stimulus patterns from controller, holds them for synchronized delivery, and drives DUT inputs with inverting logic. Use Value: Enables precise setup/hold timing (tsu = 10 ns, th = 0 ns) and sub-35 ns propagation delay for repeatable test vector execution. |
| Retrocomputing Memory Expansion | Embedded System Debug Port |
Use Scenario: Adding RAM or ROM expansion slots to vintage 8-bit computer architectures like Z80 or 6502-based systems. IC Role / Device Role / Timing Role: Bus interface register - buffers address/data/control signals between CPU and expansion bus, managing direction and isolation. Use Value: Provides true 5 V TTL compatibility, 3-state control for bus sharing, and register storage for wait-state generation or address latching. | Use Scenario: Implementing a hardware debug port on an industrial microcontroller board to monitor internal bus activity during firmware development. IC Role / Device Role / Timing Role: Passive bus snooper - OE-disabled outputs allow non-intrusive observation; inputs remain active to capture A/B bus traffic during runtime. Use Value: Use Value: Supports real-time trace capture without affecting system timing, leveraging always-enabled inputs and glitch-free select control for stable data logging. |
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 | Non-inverting output logic; otherwise identical pinout, timing, and register architecture. | Used where bus signal polarity must be preserved rather than inverted - e.g., direct replacement in existing non-inverting designs. | Select SN74ALS646ADW when system-level logic requires true (non-inverted) data transfer; verify downstream gate inputs accept non-inverted signals. |
| SN74AS648DW | Faster propagation delays (≤8.5 ns), higher drive strength (IOL = 48 mA), and extended fmax = 90 MHz - built on Advanced Schottky process. | Suitable for high-speed upgrades where timing margins are tight or higher fanout is needed; not drop-in due to different AC characteristics. | Choose SN74AS648DW for performance-critical redesigns requiring faster settling or stronger drive; validate setup/hold and clock pulse width compliance. |
Compared with SN74ALS646ADW, SN74ALS648ADW delivers inverting logic essential for certain bus termination schemes and level-shifting interfaces, while SN74AS648DW offers superior speed and drive at the cost of higher ICC (120 mA vs 57 mA) and stricter layout requirements.
Availability
SN74ALS648ADW is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy test equipment integration, retrocomputing memory expansion, and embedded debug port implementations requiring stable component supply over extended production lifecycles.
Supply support for SN74ALS648ADW 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 and embedded processing technologies with broad industrial, automotive, and consumer product portfolios.
The SN74ALS648ADW belongs to TI's legacy TTL logic family, engineered specifically for robust, pin-compatible upgrades of 74LS/74S-series bus interface components in long-lifecycle industrial and instrumentation systems.
FAQ
What is the function of the SAB and SBA pins on the SN74ALS648ADW?
The SAB and SBA pins on the SN74ALS648ADW control multiplexing between real-time (transparent) and stored data paths. SAB selects data sourced from the A-side register for output to the B bus, while SBA selects data from the B-side register for output to the A bus. Their hardware implementation eliminates decoding glitches during mode transitions, ensuring clean, metastability-free bus switching without external logic.
Does the SN74ALS648ADW support simultaneous storage from both A and B buses?
Yes, the SN74ALS648ADW supports simultaneous storage from both A and B buses. When OE is high (outputs disabled) and both CLKAB and CLKBA receive low-to-high clock transitions, data present on A1–A8 and B1–B8 is latched into their respective internal registers concurrently. This capability enables coordinated snapshot capture for handshake protocols or dual-bus monitoring applications.
What is the maximum clock frequency supported by the SN74ALS648ADW?
The SN74ALS648ADW 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 specification applies to both CLKAB and CLKBA inputs and is validated per the SDAS039F datasheet; exceeding 40 MHz may result in setup/hold violations or unreliable register capture.
Can the SN74ALS648ADW drive standard TTL loads directly?
Yes, the SN74ALS648ADW can drive standard TTL loads directly. Its output drive capability meets or exceeds standard TTL specifications: IOH = –15 mA (high-level) and IOL = 24 mA (low-level) at VCC = 4.5 V, ensuring reliable interfacing with 74LS, 74ALS, and other TTL-family inputs without external buffering.
Is the SN74ALS648ADW pin-compatible with the SN74ALS646ADW?
Yes, the SN74ALS648ADW is pin-compatible with the SN74ALS646ADW. Both devices share identical 24-pin SOIC (DW) packaging, identical pin assignments for all signals (including A/B I/O, CLKAB/CLKBA, DIR, OE, SAB/SBA, VCC, GND, and NC), and identical DC and AC timing specifications - differing only in output logic polarity (inverting vs non-inverting).
SN74ALS648ADW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 24-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tube
- Product Status:
- Active
- 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, 24mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-SOIC
SN74ALS648ADW FAQ
1.How can I place an order for SN74ALS648ADW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS648ADW 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 SN74ALS648ADW reliable?
The price and inventory of SN74ALS648ADW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS648ADW is usually 5 days.
3.What payment methods are accepted for SN74ALS648ADW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS648ADW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS648ADW?
SN74ALS648ADW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS648ADW 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 SN74ALS648ADW?
For technical support, including SN74ALS648ADW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS648ADW requirements.
6.How does Aetrix verify that SN74ALS648ADW is sourced from the original manufacturer or authorized distributors?
All SN74ALS648ADW 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 SN74ALS648ADW meets industry standards.
7.What is the process for return or replacement of SN74ALS648ADW?
All SN74ALS648ADW units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS648ADW, 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 SN74ALS648ADW part is unused and in its original packaging.
Return procedure for SN74ALS648ADW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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