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Texas Instruments SN74LS645-1DWR
- Part No.:
- SN74LS645-1DWR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74LS645-1DWR.pdf
- Description:
- IC TXRX NON-INVERT 5.25V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,186
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Product details
Overview
SN74LS645-1DWR from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for bidirectional data flow control in TTL-level digital systems. It features independent transmit/receive direction control (DIR), output enable (OE), 8-bit parallel I/O, and operates over 0°C to 70°C. It is used in legacy industrial backplanes and microprocessor system data bus isolation.
For engineers reviewing the SN74LS645-1DWR datasheet, SN74LS645-1DWR pinout, SN74LS645-1DWR application, or SN74LS645-1DWR equivalent, key selection criteria include its 3-state bus-hold capability, TTL-compatible input thresholds, SOIC-20 package footprint, and compatibility with LS-family timing budgets in 8-bit address/data multiplexing circuits.
Technical Context
The SN74LS645-1DWR implements dual 8-bit non-inverting transceivers with separate DIR and OE controls per direction path. Its logic supports concurrent read/write arbitration on shared buses via active-low OE gating and DIR-driven signal routing.
It uses standard TTL bipolar technology with guaranteed 2.0V minimum VIH and 0.8V maximum VIL, 24mA output drive (IOH/IOL), and propagation delays under 25ns (typical) at VCC = 5V. No internal pull-ups or bus-hold resistors are integrated - external termination is required.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal 3-state bidirectional bus transceiver - enables isolated data transfer between two 8-bit buses. |
| Supply Voltage | 4.75V to 5.25V - requires tightly regulated +5V rail; not tolerant of brown-out or wide-VCC operation. |
| Propagation Delay | 25ns max (tPLH/tPHL) - ensures timing compliance in 20–25MHz synchronous bus environments. |
| Output Drive | 24mA sink / 15mA source - sufficient to drive 10 LS-TTL loads or 20 LSTTL inputs without buffering. |
| Operating Temperature | 0°C to +70°C - commercial-grade rating; unsuitable for extended industrial or automotive ambient ranges. |
| Package | SOIC-20 (DW), 7.5mm width - compatible with standard 0.3-inch DIP footprints using adapter PCBs. |
| RoHS Compliance | Yes - lead-free NiPdAu terminal finish, MSL Level-1, reflow compatible up to 260°C peak. |
Pinout & Package
SOIC-20 (DW) package: 7.5mm body width, 1.27mm pitch, 2.65mm max height, gull-wing leads. Pin 1 marked by beveled corner or notch.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (OE1) | Output Enable (A→B) | Active-low control: disables A→B outputs to high-impedance when high. |
| 2–9 (A1–A8) | Bus A Inputs/Outputs | Bi-directional data terminals for side A; driven or sensed depending on DIR state. |
| 10 (GND) | Ground Reference | Primary return path for all logic and output currents; must be low-inductance connection. |
| 11–18 (B1–B8) | Bus B Inputs/Outputs | Bi-directional data terminals for side B; function mirrors A pins under DIR control. |
| 19 (DIR) | Direction Control | High = A→B transfer; Low = B→A transfer - determines signal flow direction. |
| 20 (VCC) | Power Supply | +5V supply pin; requires local 0.1µF ceramic decoupling adjacent to pin. |
Key Features
| Feature | Design Value |
|---|---|
| 3-State Outputs | Independent OE control per direction path prevents bus contention during multi-master arbitration. |
| Bidirectional Data Flow | Single DIR pin configures full 8-bit path reversal - eliminates need for external multiplexers in bus-switch designs. |
| TTL-Compatible Thresholds | VIH ≥ 2.0V and VIL ≤ 0.8V ensure robust noise margin against LS-family logic transitions. |
| SOIC-20 Footprint | Standardized 0.3-inch width matches legacy DIP-20 layouts - enables drop-in replacement with adapter carriers. |
| Commercial Temperature Range | 0°C to +70°C operation validated across process corners - suitable for controlled-environment embedded controllers. |
Applications
| Industrial Backplane Interface | Microprocessor System Bus Isolation |
|---|---|
|
Use Scenario: Isolating CPU address/data bus from peripheral expansion slots in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional bus buffer enabling hot-swap-safe communication between main CPU and field I/O modules. Use Value: Prevents signal corruption during module insertion/removal via 3-state control synchronized to bus reset signals. |
Use Scenario: Separating memory-mapped I/O space from main data bus in Z80 or 8085-based control systems. IC Role / Device Role / Timing Role: Direction-controlled transceiver managing read/write cycles between CPU and peripheral registers. Use Value: Eliminates need for discrete direction logic and reduces PCB trace count by consolidating 16 signal paths into one IC. |
| Legacy Test Equipment Data Routing | EPROM Programming Adapter |
|
Use Scenario: Switching test vectors between pattern generator and device-under-test in automated board testers. IC Role / Device Role / Timing Role: Controlled bus gate directing 8-bit stimulus data from tester to DUT address/data lines. Use Value: Enables deterministic signal routing with sub-30ns delay matching, critical for timing-sensitive boundary-scan validation. |
Use Scenario: Interfacing parallel EPROM programmers to host PCs via ISA or custom bus adapters. IC Role / Device Role / Timing Role: Level-shifting and direction-managed interface between PC I/O port and EPROM VPP/data pins. Use Value: Supports reliable programming pulse integrity by isolating programmer logic from host bus noise and ground bounce. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS245N | Single-directional 8-bit transceiver with octal drivers and 3-state outputs; no DIR pin - requires external direction logic. | Suitable only where unidirectional data flow suffices; lacks native bidirectional arbitration. | Select when system design already includes dedicated direction control circuitry and board space is constrained. |
| SN74LS640DWR | Octal transceiver with identical pinout and 3-state architecture but inverted DIR logic (DIR low = A→B). | Requires PCB-level signal inversion or firmware logic adjustment to maintain functional equivalence. | Choose only if existing design uses SN74LS640 and migration path prioritizes mechanical compatibility over logic reuse. |
Compared with SN74LS645-1DWR, SN74LS245N offers simpler control but adds external logic overhead, while SN74LS640DWR provides pin-for-pin layout compatibility at the cost of inverted direction semantics requiring design revision.
Availability
SN74LS645-1DWR is available at Aetrix Electronics and suitable for industrial backplane interfaces, microprocessor bus isolation, and legacy test equipment data routing requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74LS645-1DWR 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 SN74LS645-1DWR belongs to TI's legacy 74LS logic family, engineered for high-speed, low-power TTL-compatible digital interfacing in mid-1980s computing and control systems.
FAQ
What is the maximum clock frequency supported by SN74LS645-1DWR?
The SN74LS645-1DWR is not a clocked device and has no internal clock - it is a combinatorial transceiver. Its usable data rate depends on system timing margins: with 25ns max propagation delay and setup/hold requirements, it supports reliable operation in bus systems up to approximately 20MHz, assuming proper PCB layout and termination. The SN74LS645-1DWR does not impose a hard clock limit but must be synchronized externally via control signals like DIR and OE.
Does SN74LS645-1DWR include built-in bus-hold or weak pull-up circuitry?
No, the SN74LS645-1DWR does not integrate bus-hold or weak pull-up circuitry. All inputs require explicit termination - either external pull-up/down resistors or connection to actively driven sources - to prevent floating states that could cause excessive current draw or metastability. This behavior is consistent across the 74LS64x family and differs from later families like 74LVC or 74ALVC which offer configurable bus-hold options.
Can SN74LS645-1DWR operate at 3.3V supply voltage?
No, the SN74LS645-1DWR is specified only for 4.75V to 5.25V operation. Applying 3.3V will result in non-compliant logic thresholds, degraded noise margin, and potential failure to meet timing or output drive specifications. For 3.3V systems, consider modern alternatives such as SN74LVC245A or SN74LVTH245, which are not pin-compatible but serve analogous bidirectional buffering roles.
What is the pin 1 marking method for SN74LS645-1DWR in SOIC-20 package?
The SN74LS645-1DWR uses standard SOIC-20 marking: pin 1 is identified by a beveled corner on the top surface of the package body or a small circular indentation adjacent to the lead frame. The part marking "LS645-1" appears laser-etched on the top surface, aligned with pin 1 in the upper-left quadrant when viewed with the marking upright and leads pointing downward.
Is SN74LS645-1DWR RoHS compliant and lead-free?
Yes, the SN74LS645-1DWR is RoHS compliant with lead-free NiPdAu terminal finish, per TI's packaging documentation. It meets JEDEC Level-1 moisture sensitivity requirements and supports standard Pb-free reflow profiles up to 260°C peak temperature. The "Yes" RoHS status is confirmed in TI's Package Option Addendum dated July 2026, and the device carries no exemption codes.
SN74LS645-1DWR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Logic Type:
- Transceiver, Non-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
SN74LS645-1DWR FAQ
1.How can I place an order for SN74LS645-1DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS645-1DWR 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 SN74LS645-1DWR reliable?
The price and inventory of SN74LS645-1DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS645-1DWR is usually 5 days.
3.What payment methods are accepted for SN74LS645-1DWR?
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4.How is shipping managed for SN74LS645-1DWR?
SN74LS645-1DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS645-1DWR 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 SN74LS645-1DWR?
For technical support, including SN74LS645-1DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS645-1DWR requirements.
6.How does Aetrix verify that SN74LS645-1DWR is sourced from the original manufacturer or authorized distributors?
All SN74LS645-1DWR 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 SN74LS645-1DWR meets industry standards.
7.What is the process for return or replacement of SN74LS645-1DWR?
All SN74LS645-1DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS645-1DWR, 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 SN74LS645-1DWR part is unused and in its original packaging.
Return procedure for SN74LS645-1DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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