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Texas Instruments SN74AS640NS
- Part No.:
- SN74AS640NS
- Manufacturer:
- Texas Instruments
- Package:
- -
- Datasheet:
-
SN74AS640NS.pdf
- Description:
- IC BUS TRANSCEIVER 8BIT 20SO
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Inventory:1,120
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Product details
Overview
SN74AS640NS from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for asynchronous bidirectional data transfer between A and B buses in TTL-compatible systems. It features inverting logic, 20-pin PDIP (N) package, ±15 mA high-level output current, 64 mA low-level output current, and operates from 0°C to 70°C.
For engineers reviewing the SN74AS640NS datasheet, SN74AS640NS pinout, SN74AS640NS application, or SN74AS640NS equivalent, this page delivers verified electrical specs, directional control behavior, 3-state isolation timing, and direct replacement guidance for legacy TTL bus interface designs.
Technical Context
The SN74AS640NS implements a dual-rail bidirectional transceiver architecture controlled by DIR (direction) and OE (output enable) inputs. Its inverting logic path ensures signal polarity inversion during A↔B data transfer, and its 3-state outputs fully isolate buses when OE is high.
It supports TTL-level input thresholds (VIL = 0.8 V, VIH = 2 V), delivers VOL ≤ 0.55 V at IOL = 64 mA, and achieves propagation delays as low as 2 ns (tPHL) and 2 ns (tPLH) under loaded conditions (CL = 50 pF). Power supply range is strictly 4.5 V to 5.5 V.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - Must be regulated within this window for guaranteed TTL-compatible operation and output drive strength. |
| IOH / IOL | –15 mA / 64 mA - Sinks up to 64 mA per output, enabling direct drive of multiple TTL loads without external buffers. |
| tPHL / tPLH | 2 ns / 7 ns - Propagation delay from input to output enables high-speed bus arbitration in 8-bit parallel systems. |
| VOL @ IOL=64mA | ≤ 0.55 V - Ensures solid logic-low margin across full temperature range (0°C to 70°C) and load variation. |
| VIH / VIL | 2 V / 0.8 V - Matches standard TTL input thresholds, allowing seamless integration with 74LS/74AS logic families. |
| ICC (Outputs Low) | 123 mA - Peak supply current during active bus driving; requires local decoupling and thermal consideration in dense layouts. |
| 3-State Enable Time | tPZH = 8 ns max - Fast output disable ensures clean bus release during direction switching or arbitration cycles. |
Pinout & Package
SN74AS640NS uses a 20-pin plastic DIP (PDIP-N) package with 300-mil width, 2.54 mm pitch, and through-hole mounting. Pin 1 is marked by a notch or dot at the top-left corner.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | DIR | Direction control: LOW enables B→A transfer; HIGH enables A→B transfer. |
| 2–9 | A1–A8 | Input/output port A - bidirectional data lines connected to one bus segment. |
| 10 | GND | Ground reference for all logic and power domains. |
| 11–18 | B1–B8 | Input/output port B - bidirectional data lines connected to second bus segment. |
| 19 | OE | Output enable: LOW activates transceiver; HIGH forces all A/B pins into high-impedance state. |
| 20 | VCC | +5 V power supply - must be decoupled locally with ≥0.1 µF ceramic capacitor. |
Key Features
| Feature | Design Value |
|---|---|
| Inverting bidirectional logic | Signal polarity is inverted on each pass (A→B or B→A), simplifying level-shifting in mixed-logic systems. |
| 64 mA sink capability per output | Drives up to 16 standard TTL inputs directly, eliminating need for bus drivers in many industrial backplane applications. |
| Sub-10 ns 3-state disable time | tPLZ = 13 ns max ensures rapid bus release, preventing contention during multi-master arbitration. |
| TTL-compatible input thresholds | VIL = 0.8 V and VIH = 2 V guarantee interoperability with legacy 74LS, 74ALS, and 74AS logic families. |
| Industrial temperature range | Rated for 0°C to 70°C operation - suitable for commercial and industrial embedded control systems with passive cooling. |
Applications
| Industrial Backplane Interface | Legacy System Bus Extension |
|---|---|
|
Use Scenario: Interfacing microcontroller local bus to a 20-slot ISA-style backplane carrying multiple peripheral cards. IC Role / Device Role / Timing Role: Bidirectional octal transceiver managing data flow between CPU address/data bus and expansion slot bus, controlled by ISA I/O channel signals. Use Value: Enables synchronous read/write handshaking with sub-10 ns timing margins, supporting 8 MHz ISA bus clock rates without added wait states. |
Use Scenario: Extending a vintage 8-bit computer's internal bus to external memory or I/O modules via ribbon cable. IC Role / Device Role / Timing Role: Isolating and translating signals between mainboard and daughterboard while preserving TTL voltage levels and fanout. Use Value: 64 mA drive strength maintains signal integrity over 30 cm flat-cable runs, eliminating termination resistors and reducing BOM count. |
| Test Equipment Data Switching | Programmable Logic Controller I/O Hub |
|
Use Scenario: Routing test patterns between pattern generator and DUT in automated test equipment using shared bus architecture. IC Role / Device Role / Timing Role: Directionally configurable bus switch controlled by FPGA sequencer to alternate stimulus/response paths. Use Value: 3-state isolation (tPZH ≤ 8 ns) prevents signal leakage during reconfiguration, ensuring test vector accuracy and repeatability. |
Use Scenario: Aggregating discrete sensor inputs and actuator outputs onto a central PLC CPU bus in factory automation cabinets. IC Role / Device Role / Timing Role: Buffering and isolating field-side I/O signals from noisy control bus, with DIR tied to scan-cycle phase. Use Value: High noise immunity (VIK = –1.2 V) and robust 3-state hold suppress ground bounce and crosstalk in electrically harsh environments. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bidirectional bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS640BN | Lower drive strength: IOL = 24 mA (vs. 64 mA); slower tPHL/tPLH (10/11 ns vs. 6/7 ns); same pinout and logic function. | Suitable only for low-fanout, lower-speed systems (< 4 MHz bus clock); not recommended for long traces or heavy TTL loading. | Select SN74ALS640BN only if power consumption (ICC = 55 mA max) is prioritized over speed and drive capability. |
| 74F640SC | Faster: tPHL/tPLH = 4.5/5.5 ns; higher ICC (140 mA); non-inverting logic; identical 20-pin SOIC/PDIP footprint. | Requires logic inversion externally if system design assumes inverting path; better for high-frequency (>20 MHz) backplanes with tight timing budgets. | Choose 74F640SC when speed is critical and inverting behavior can be accommodated in firmware or layout routing. |
Compared with SN74ALS640BN and 74F640SC, the SN74AS640NS uniquely balances high drive (64 mA), moderate speed (6–7 ns), and inverting logic in a legacy-compatible PDIP package-making it optimal for retrofitting aging industrial controllers where signal polarity and physical form factor are fixed constraints.
Availability
SN74AS640NS is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus extensions, automated test equipment data routing, and programmable logic controller I/O hubs requiring stable component supply and long-term obsolescence management.
Supply support for SN74AS640NS 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, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The SN74AS640NS belongs to TI's 74AS advanced Schottky TTL logic family, engineered for high-speed, high-drive bus interfacing in systems where compatibility with legacy TTL infrastructure is mandatory.
FAQ
What is the maximum operating temperature for the SN74AS640NS?
The SN74AS640NS is characterized for operation from 0°C to 70°C. This industrial temperature range is specified in the official Texas Instruments datasheet SDAS122A and applies to all SN74AS640 variants in PDIP (N) packaging. Operation outside this range may result in undefined timing or output behavior.
Does the SN74AS640NS support non-inverting data transfer?
No, the SN74AS640NS implements inverting logic: data transferred from A to B or B to A is inverted. This is inherent to its internal circuit architecture and confirmed in the function table and logic diagram of the SN74AS640NS datasheet. External inverters would be required for non-inverting operation.
Can the SN74AS640NS be used with a 3.3 V supply?
No. The SN74AS640NS requires a 4.5 V to 5.5 V supply (VCC) and is not rated for 3.3 V operation. Its input thresholds (VIH = 2 V, VIL = 0.8 V) and output drive characteristics are optimized for 5 V TTL systems. Using 3.3 V will result in unreliable logic levels and insufficient output current.
What is the meaning of the "NS" suffix in SN74AS640NS?
The "NS" suffix in SN74AS640NS is a historical package designation used by Texas Instruments for the plastic DIP (PDIP) variant with 300-mil width. It corresponds to the "N" package type in TI's ordering nomenclature (e.g., SN74AS640N), and confirms the device uses a through-hole 20-pin dual in-line package.
Is the SN74AS640NS pin-compatible with the SN74ALS640BN?
Yes, the SN74AS640NS and SN74ALS640BN share identical 20-pin PDIP (N) packaging, pin assignments, and functional pin definitions (DIR, OE, A1–A8, B1–B8, VCC, GND). However, they differ electrically: SN74AS640NS provides higher drive (64 mA vs. 24 mA) and faster timing (6–7 ns vs. 10–11 ns).
SN74AS640NS Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- -
- Number of Elements:
- -
- Number of Bits per Element:
- -
- Input Type:
- -
- Output Type:
- -
- Current - Output High, Low:
- -
- Voltage - Supply:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- -
- Supplier Device Package:
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SN74AS640NS FAQ
1.How can I place an order for SN74AS640NS through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS640NS 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 SN74AS640NS reliable?
The price and inventory of SN74AS640NS are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS640NS is usually 5 days.
3.What payment methods are accepted for SN74AS640NS?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS640NS transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS640NS?
SN74AS640NS orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS640NS 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 SN74AS640NS?
For technical support, including SN74AS640NS datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS640NS requirements.
6.How does Aetrix verify that SN74AS640NS is sourced from the original manufacturer or authorized distributors?
All SN74AS640NS 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 SN74AS640NS meets industry standards.
7.What is the process for return or replacement of SN74AS640NS?
All SN74AS640NS units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS640NS, 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 SN74AS640NS part is unused and in its original packaging.
Return procedure for SN74AS640NS:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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