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Texas Instruments SN74AS648DW
- Part No.:
- SN74AS648DW
- Manufacturer:
- Texas Instruments
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74AS648DW.pdf
- Description:
- IC TXRX INVERT 5.5V 24SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,361
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Product details
Overview
SN74AS648DW from Texas Instruments is an octal bus transceiver and register IC with 3-state outputs, inverting data path, dual-bus register storage, and real-time/stored data multiplexing capability. It operates at up to 90 MHz clock frequency, supports 5 V supply, delivers 48 mA low-level output drive, and is rated for 0°C to 70°C industrial temperature range.
For engineers reviewing the SN74AS648DW datasheet, SN74AS648DW pinout, SN74AS648DW application, or SN74AS648DW equivalent, this device is selected for high-speed bidirectional bus isolation, registered data handoff between A/B buses, glitch-free multiplexed bus management, and legacy TTL-compatible system interconnects requiring stored-data arbitration.
Technical Context
The SN74AS648DW integrates eight independent D-type flip-flops per bus (A and B), asynchronous 3-state output control via OE, directional control via DIR, and dual select inputs (SAB/SBA) that enable seamless switching between transparent and registered data paths without decoding glitches. Its architecture supports simultaneous storage on both buses and selective transfer of stored or real-time data to either bus.
It uses advanced Schottky-clamped bipolar (AS) technology for improved speed over ALS variants, with propagation delays as low as 1 ns (tPHL A→B), sub-10 ns clock-to-output timing, and robust noise immunity via defined VIH/VIL thresholds (2.0 V / 0.8 V) and input hysteresis.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal bus transceiver with dual independent registers and inverting 3-state outputs |
| Max clock frequency | 90 MHz - enables high-throughput synchronous bus handoff in real-time systems |
| IOL (max) | 48 mA - drives heavy capacitive loads or multiple TTL inputs without external buffers |
| VCC operating range | 4.5 V to 5.5 V - compatible with standard 5 V logic rails and tolerant of supply ripple |
| Propagation delay (A→B) | 1 ns (min) to 7 ns (max) - ensures tight timing margins in high-speed backplane or memory interface designs |
| Operating temperature | 0°C to 70°C - qualified for commercial/industrial embedded control and instrumentation applications |
| Input voltage thresholds | VIH = 2.0 V, VIL = 0.8 V - provides 0.4 V noise margin against TTL-level signal degradation |
Pinout & Package
SN74AS648DW is housed in a 24-pin SOIC (DW) package with 300-mil width, surface-mount footprint, and JEDEC MS-013 compliant dimensions (7.50 mm × 15.40 mm). Pin 1 is marked by a beveled corner or dot; pin count and layout match industry-standard 24-pin SOIC footprints.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | CLKAB | Clocks data from A bus into A-side register on rising edge |
| 2 | SAB | Selects between real-time A data (L) or stored A data (H) for output to B bus |
| 3 | DIR | Controls direction: L = B→A, H = A→B during transceiver mode |
| 4–11 | A1–A8 | 8-bit bidirectional A-bus I/O port with internal register storage |
| 12 | GND | Power ground reference for all logic and I/O circuits |
| 13–20 | B1–B8 | 8-bit bidirectional B-bus I/O port with internal register storage |
| 21 | OE | Output enable: active-low; disables all 3-state outputs when high |
| 22 | SBA | Selects between real-time B data (L) or stored B data (H) for output to A bus |
| 23 | CLKBA | Clocks data from B bus into B-side register on rising edge |
| 24 | VCC | +5 V supply rail for core logic and output drivers |
Key Features
| Feature | Design Value |
|---|---|
| Inverting data path | Ensures signal polarity consistency across registered transfers, eliminating need for external inverters in feedback or handshake loops |
| Glitch-free select control (SAB/SBA) | Hardware-decoded multiplexer avoids metastability and transient shorts during real-time ↔ stored data transitions |
| Dual independent registers | Enables concurrent capture of A and B bus data, supporting ping-pong buffering and deterministic latency scheduling |
| 3-state outputs with fast enable/disable | tPZH/tPLZ ≤ 9 ns ensures minimal bus contention window during direction or enable switching |
| High-current drive (48 mA IOL) | Directly interfaces with legacy TTL loads, LED indicators, or long trace runs without fanout buffers |
Applications
| Industrial PLC Backplane Interface | Legacy System Bus Arbitration |
|---|---|
Use Scenario: Isolating and synchronizing data flow between CPU and I/O modules in modular programmable logic controllers using parallel backplanes. IC Role / Device Role / Timing Role: Acts as registered bidirectional bus transceiver, capturing CPU writes into B-register while forwarding sensor reads from A-register to CPU on next cycle. Use Value: Eliminates timing skew between distributed modules by registering data at both ends, enabling deterministic 90 MHz bus cycles across meter-long traces. | Use Scenario: Managing shared address/data bus between multiple legacy microprocessors (e.g., Z80, 8085) and peripheral controllers in retro-computing or test equipment. IC Role / Device Role / Timing Role: Provides direction-controlled, OE-gated bus isolation with stored-data hold capability during processor context switches. Use Value: Prevents bus contention during multi-master arbitration by latching prior state and enabling glitch-free handoff via SAB/SBA controls. |
| High-Speed Memory Interface Buffer | Test Equipment Signal Routing Matrix |
Use Scenario: Interfacing FPGA-based memory controllers to parallel SRAM or EPROM devices with strict setup/hold timing requirements. IC Role / Device Role / Timing Role: Registers address/data lines on CLKAB/CLKBA edges to meet tSU/th specs of older memories, then forwards synchronized bursts via DIR/OE control. Use Value: Compensates for FPGA I/O delay variability and extends maximum reliable memory access frequency to 90 MHz. | Use Scenario: Configurable signal routing in automated test systems where stimulus/response paths must be dynamically reconfigured without software intervention. IC Role / Device Role / Timing Role: Functions as hardware-programmable 8-bit crosspoint switch with nonvolatile register hold, controlled by front-panel DIP switches or microcontroller GPIO. Use Value: Enables zero-latency path reconfiguration via SAB/SBA selects, bypassing firmware polling delays and supporting sub-microsecond test sequence changes. |
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 |
|---|---|---|---|
| SN74ALS648ADW | ALS family: lower speed (40 MHz max), lower drive (24 mA IOL), higher propagation delay (≤20 ns A→B) | Suitable for cost-sensitive, lower-frequency systems where power consumption and noise immunity are prioritized over speed | Choose when 90 MHz operation is unnecessary and board-level noise margins require slower edge rates |
| SN74AS646DW | Non-inverting data path; otherwise identical pinout, timing, and drive capability | Required where signal polarity must be preserved end-to-end (e.g., in feedback control loops or differential pair termination) | Select only when inverting behavior of SN74AS648DW conflicts with system-level logic polarity requirements |
Compared with SN74ALS648ADW, SN74AS648DW delivers 2.25× higher clock rate and 2× stronger drive for demanding real-time interfaces; versus SN74AS646DW, it provides inverted output polarity essential for certain handshake protocols and level-shifting topologies.
Availability
SN74AS648DW is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy system bus arbitration, high-speed memory interface buffering, and test equipment signal routing matrices requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74AS648DW 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 specializing in analog, embedded processing, and logic solutions, with decades of heritage in TTL and advanced logic families.
The SN74AS648DW belongs to TI's AS-series advanced Schottky logic product line, designed specifically for high-speed, low-noise digital system interconnects in industrial, test, and computing applications requiring precise timing and robust drive capability.
FAQ
What is the primary function of the SN74AS648DW in a digital system?
The SN74AS648DW serves as an octal bus transceiver with dual independent registers and inverting 3-state outputs. It enables bidirectional data transfer between two 8-bit buses (A and B), supports real-time or registered data routing via SAB/SBA controls, and provides glitch-free multiplexing-making it ideal for high-speed bus arbitration, memory interfacing, and industrial backplane designs where deterministic timing and strong drive are critical. The SN74AS648DW is especially valued for its 90 MHz clock capability and 48 mA output sink current.
Does the SN74AS648DW support both real-time and stored data modes simultaneously?
Yes-the SN74AS648DW supports concurrent real-time and stored data operations. Its dual independent registers allow A-bus and B-bus data to be captured simultaneously on rising edges of CLKAB and CLKBA, respectively. The SAB and SBA inputs then independently select whether real-time or stored data appears on the opposite bus, enabling mixed-mode operation-for example, real-time A→B transfer while outputting stored B data to A. This capability is intrinsic to the SN74AS648DW architecture and requires no external logic.
What is the significance of the inverting data path in the SN74AS648DW compared to the SN74AS646DW?
The SN74AS648DW implements an inverting data path, meaning output data is logically complemented relative to input data during transceiver operation. This differs from the non-inverting SN74AS646DW and is essential in applications requiring signal inversion-such as matching complementary bus protocols, implementing active-low handshake signals, or compensating for inverter stages elsewhere in the signal chain. The inversion is hardwired in the SN74AS648DW silicon and cannot be disabled; system design must account for this polarity behavior.
Can the SN74AS648DW operate reliably at 5.5 V supply voltage?
Yes-the SN74AS648DW is fully specified for operation across VCC = 4.5 V to 5.5 V per its recommended operating conditions. Electrical characteristics-including VOH, VOL, propagation delays, and IOL-are guaranteed over this full range. At 5.5 V, the SN74AS648DW maintains 48 mA low-level output drive and meets all timing parameters, making it suitable for systems with nominal 5 V rails that experience transient overshoot or regulation tolerance.
How does the SN74AS648DW prevent bus contention during direction or output-enable transitions?
The SN74AS648DW prevents bus contention through fast, controlled 3-state enable/disable timing: tPZH and tPHZ are guaranteed ≤9 ns, ensuring outputs enter high-impedance state before new drivers activate. Combined with DIR-synchronized output gating and OE priority over DIR, the SN74AS648DW guarantees that only one bus (A or B) drives at any time-even during dynamic reconfiguration. This behavior is inherent to the SN74AS648DW's internal control logic and eliminates need for external arbitration circuitry.
SN74AS648DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AS
- Package/Case:
- 24-SOIC (0.295", 7.50mm Width)
- 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:
- Surface Mount
- Supplier Device Package:
- 24-SOIC
SN74AS648DW FAQ
1.How can I place an order for SN74AS648DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS648DW 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 SN74AS648DW reliable?
The price and inventory of SN74AS648DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS648DW is usually 5 days.
3.What payment methods are accepted for SN74AS648DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS648DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS648DW?
SN74AS648DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS648DW 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 SN74AS648DW?
For technical support, including SN74AS648DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS648DW requirements.
6.How does Aetrix verify that SN74AS648DW is sourced from the original manufacturer or authorized distributors?
All SN74AS648DW 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 SN74AS648DW meets industry standards.
7.What is the process for return or replacement of SN74AS648DW?
All SN74AS648DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS648DW, 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 SN74AS648DW part is unused and in its original packaging.
Return procedure for SN74AS648DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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