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Texas Instruments SN74LS640-1DW
- Part No.:
- SN74LS640-1DW
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74LS640-1DW.pdf
- Description:
- IC TXRX INVERT 5.25V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:379
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Product details
Overview
SN74LS640-1DW from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for bidirectional data flow control in TTL-level parallel bus systems. It features 8-bit non-inverting data paths, independent output-enable (OE) and direction (DIR) controls, and operates over 0°C to 70°C. It supports high-speed bus interfacing in legacy industrial controllers and retro-computing backplanes.
For engineers reviewing the SN74LS640-1DW datasheet, SN74LS640-1DW pinout, SN74LS640-1DW application, or SN74LS640-1DW equivalent, key selection criteria include its 3-state output drive capability, dual-control logic (DIR/OE), SOIC-20 package footprint, TTL-compatible input thresholds, and compatibility with LS-family timing budgets in synchronous bus architectures.
Technical Context
This device implements two independent 4-bit bidirectional buffers per package, each with separate DIR and OE inputs-enabling full 8-bit bus arbitration without external gating. Its output stage uses standard TTL totem-pole drivers with guaranteed 24 mA sink and 15 mA source capability at VCC = 5 V.
Propagation delay is specified at tPLH/tPHL ≤ 25 ns (max) under standard load conditions (RL = 400 Ω, CL = 15 pF), and it meets all DC electrical specifications of the 74LS logic family, including input clamp diodes and noise margins ≥ 0.4 V.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS TTL - ensures interoperability with legacy LS-based systems and predictable fanout (up to 20 LS loads). |
| Data Width | 8-bit bidirectional - enables full byte-wide bus transfer between microprocessor data buses and peripheral subsystems. |
| Output Type | 3-state (high-impedance) - allows multiple devices to share a common bus without contention when OE is inactive. |
| Control Inputs | DIR (direction) + OE (output enable) - provides independent control of data flow direction and bus release timing. |
| Supply Voltage | VCC = 4.75 V to 5.25 V - matches standard TTL power rail tolerances and avoids level-shifting in mixed-logic designs. |
| Propagation Delay | tPD ≤ 25 ns (max) - supports bus clock rates up to ~20 MHz in point-to-point configurations with minimal skew. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded applications including test equipment and industrial HMIs. |
Pinout & Package
SN74LS640-1DW is housed in a 20-pin Small Outline Integrated Circuit (SOIC) package with 1.27 mm pitch, 7.5 mm body width, and 2.65 mm max height. Pin 1 is marked by a beveled corner or dot; the package is RoHS-compliant with NiPdAu lead finish and MSL Level-1 rating.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction control input | High = A→B data flow; Low = B→A - determines signal path polarity for all 8 channels simultaneously. |
| 2–9 (A1–A8) | Port A data terminals | Connect to primary bus (e.g., CPU data bus); driven or received depending on DIR state. |
| 10 (GND) | Ground reference | Common return for all internal logic and I/O; must be low-inductance connection for noise immunity. |
| 11–18 (B1–B8) | Port B data terminals | Connect to secondary bus (e.g., memory or peripheral interface); complementary to Port A. |
| 19 (OE) | Output enable input | Low = outputs active; High = all outputs in high-impedance - used for bus arbitration and power-down sequencing. |
| 20 (VCC) | Positive supply | 5 V nominal supply; decoupling capacitor (0.1 µF ceramic) required within 10 mm of this pin. |
Key Features
| Feature | Design Value |
|---|---|
| Octal bidirectional data path | Enables single-chip replacement of four discrete 74LS245 transceivers, reducing board area and interconnect complexity. |
| Independent DIR and OE controls | Allows asynchronous bus release (OE high while DIR toggles), preventing glitches during mode transitions. |
| TTL-compatible input thresholds | VIL ≤ 0.8 V / VIH ≥ 2.0 V - ensures reliable interfacing with 74LS, 74S, and microcontroller GPIO without level shifters. |
| 3-state output leakage & drive | IOZ ≤ ±10 µA (high-Z), IOL = –24 mA / IOH = 15 mA - supports robust bus loading and hot-swap tolerance in modular systems. |
| SOIC-20 footprint compatibility | Matches industry-standard 0.300" wide SOIC layout; compatible with automated SMT placement and reflow profiles (Level-1). |
Applications
| Industrial PLC Backplane Interface | Retrocomputing Bus Expansion |
|---|---|
|
Use Scenario: Interfacing a Z80 CPU bus to isolated I/O modules in a DIN-rail mounted programmable logic controller. IC Role / Device Role / Timing Role: Bidirectional data bridge between CPU address/data bus and opto-isolated peripheral cards; synchronizes with WAIT and MREQ signals. Use Value: Eliminates need for discrete bus switches and reduces propagation delay variance across 8-bit lanes versus cascaded 4-bit parts. |
Use Scenario: Adding RAM expansion to a 1980s-era home computer using its original 8-bit data bus architecture. IC Role / Device Role / Timing Role: Transceiver enabling shared access between main CPU and expansion card memory space; controlled by address decoder outputs. Use Value: Maintains strict LS-family timing alignment (tPD ≤ 25 ns), preserving original system timing margins without redesign. |
| Legacy Test Equipment Data Link | Embedded Instrumentation Subsystem |
|
Use Scenario: Connecting GPIB or IEEE-488 controller logic to internal diagnostic bus in benchtop oscilloscopes and logic analyzers. IC Role / Device Role / Timing Role: Isolates controller-side logic from instrument backplane during self-test sequences via OE-controlled tri-state. Use Value: Prevents bus contention during firmware updates and calibration routines while retaining full 8-bit throughput. |
Use Scenario: Managing communication between an ARM Cortex-M0+ host and legacy sensor array using parallel status/data registers. IC Role / Device Role / Timing Role: Protocol translator between modern MCU GPIO and vintage parallel sensor interface; DIR set statically, OE pulsed for burst reads. Use Value: Provides deterministic setup/hold timing for slow peripherals without software bit-banging overhead. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS245N | Single-directional 8-bit transceiver with separate A→B and B→A enable pins; no DIR input. | Requires external logic to manage bidirectional flow; less flexible for dynamic bus arbitration. | Choose when fixed unidirectional data paths simplify control logic and reduce gate count. |
| SN74LS642-1DW | Octal transceiver with open-collector outputs instead of 3-state; requires external pull-up resistors. | Suitable for wired-AND bus structures (e.g., interrupt lines), not general-purpose bidirectional data buses. | Prefer only when implementing shared interrupt or acknowledge signaling where active-low open-collector behavior is required. |
Compared with SN74LS245N and SN74LS642-1DW, the SN74LS640-1DW uniquely integrates bidirectional control and 3-state outputs in one SOIC-20 package-making it the only direct solution for compact, low-glitch, fully controllable 8-bit bus bridging in commercial-temperature legacy systems.
Availability
SN74LS640-1DW is available at Aetrix Electronics and suitable for industrial PLC backplane interfaces, retrocomputing bus expansion, and legacy test equipment data links requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74LS640-1DW 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 with deep heritage in TTL and bipolar logic families.
The SN74LS640-1DW belongs to TI's legacy 74LS logic portfolio, engineered specifically for reliability and timing consistency in commercial-grade industrial control, instrumentation, and computing systems built before 1990.
FAQ
What is the function of the DIR pin on the SN74LS640-1DW?
The DIR (direction) pin on the SN74LS640-1DW controls the data flow direction across all eight channels: when DIR is high, data passes from Port A to Port B; when low, data flows from Port B to Port A. This pin operates independently of OE and must be stable before enabling outputs to avoid bus contention. The SN74LS640-1DW relies on this dual-control scheme for glitch-free bidirectional operation in synchronous bus environments.
Is SN74LS640-1DW still in production and supported by Texas Instruments?
No-SN74LS640-1DW is officially marked "Obsolete" in TI's packaging addendum, with no active production or new shipments. However, Aetrix Electronics maintains verified legacy stock with full traceability and extended lifecycle support. The SN74LS640-1DW remains viable for repair, maintenance, and low-volume continuation builds where form-fit-function equivalence is critical.
Can SN74LS640-1DW replace SN74LS245 in existing designs?
Not directly-SN74LS640-1DW has different pinout, control logic (DIR vs. separate A/B enables), and internal architecture. While both are octal transceivers, the SN74LS640-1DW requires redesign of control signal routing and timing. For drop-in replacement, SN74LS245N or SN74LS245DWR are functionally and pin-compatible alternatives to SN74LS245; SN74LS640-1DW serves distinct bidirectional arbitration use cases.
What is the maximum clock rate supported by SN74LS640-1DW in a bus application?
The SN74LS640-1DW does not contain an internal clock; it is asynchronous. Its usable data rate depends on propagation delay (≤25 ns) and system-level timing margins. In practice, it reliably supports bus cycles down to 50 ns period (~20 MHz), assuming proper PCB layout, termination, and load capacitance ≤15 pF. The SN74LS640-1DW is commonly deployed in 4–8 MHz Z80 and 6502 systems where setup/hold times are met with margin.
Does SN74LS640-1DW require external pull-up resistors on its outputs?
No-SN74LS640-1DW features standard totem-pole 3-state outputs, not open-collector. Pull-ups are unnecessary unless driving long traces susceptible to ringing or interfacing with legacy NMOS inputs requiring elevated VIH. Unlike SN74LS642-1DW (open-collector), the SN74LS640-1DW drives both logic high and low actively, simplifying design and reducing component count.
SN74LS640-1DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Bulk
- 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:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74LS640-1DW FAQ
1.How can I place an order for SN74LS640-1DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS640-1DW 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 SN74LS640-1DW reliable?
The price and inventory of SN74LS640-1DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS640-1DW is usually 5 days.
3.What payment methods are accepted for SN74LS640-1DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS640-1DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS640-1DW?
SN74LS640-1DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS640-1DW 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 SN74LS640-1DW?
For technical support, including SN74LS640-1DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS640-1DW requirements.
6.How does Aetrix verify that SN74LS640-1DW is sourced from the original manufacturer or authorized distributors?
All SN74LS640-1DW 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 SN74LS640-1DW meets industry standards.
7.What is the process for return or replacement of SN74LS640-1DW?
All SN74LS640-1DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS640-1DW, 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 SN74LS640-1DW part is unused and in its original packaging.
Return procedure for SN74LS640-1DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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