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Texas Instruments SN74LS171D
- Part No.:
- SN74LS171D
- Manufacturer:
- Texas Instruments
- Category:
- Flip Flops
- Package:
- -
- Datasheet:
-
SN74LS171D.pdf
- Description:
- D FLIP-FLOP, LS SERIES TTL
- Quantity:
- Payment:
- Shipping:
Inventory:1,637
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Product details
Overview
SN74LS171D from Texas Instruments is a 4-bit synchronous binary counter with parallel load and clear functionality, featuring TTL logic family compatibility, 15 ns typical propagation delay (tPLH/tPHL), and operation across 4.75 V to 5.25 V supply range. It serves as a programmable counter in digital control sequencers and test equipment timing circuits.
For engineers reviewing the SN74LS171D datasheet, SN74LS171D pinout, SN74LS171D application, or SN74LS171D equivalent, key selection considerations include synchronous reset behavior, parallel data loading capability, clock enable control, and TTL-level input/output voltage thresholds.
Technical Context
The SN74LS171D implements four edge-triggered D-type flip-flops with common clock and master reset, supporting synchronous counting via internal ripple-carry logic. Its parallel load function allows immediate presetting of all four bits on the rising edge of CLK when LOAD is low.
It features active-low asynchronous clear (CLR̅), active-low load enable (LOAD̅), and clock enable (CLKEN) that gates the clock input. Output drive capability meets standard TTL fan-out specifications (10 LSTTL loads).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | LS-TTL - ensures compatibility with legacy 74LS-series systems and predictable noise margins |
| Count Width | 4-bit - supports modulo-16 counting or direct 4-bit register storage |
| Propagation Delay | 15 ns max (tPLH/tPHL) - enables reliable operation up to ~30 MHz clock frequency in cascaded configurations |
| Supply Voltage | 4.75 V to 5.25 V - requires regulated +5 V rail; not tolerant of undervoltage or overvoltage conditions |
| Operating Temperature | 0 °C to +70 °C - rated for commercial-grade environments only |
| Output Drive | IOH = –0.4 mA / IOL = 8 mA - sufficient to drive 10 standard LSTTL inputs without buffering |
Pinout & Package
SN74LS171D is housed in a 16-pin plastic dual in-line package (PDIP) with standard through-hole mounting and 0.3-inch body width.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (CLR̅) | Asynchronous Clear Input | Active-low reset; forces all Q outputs low independently of clock or load state |
| 2–5 (P0–P3) | Parallel Data Inputs | Accept 4-bit binary value loaded synchronously when LOAD̅ = low and CLK rises |
| 6 (CLKEN) | Clock Enable Input | High disables clock action; low permits counting or loading on next CLK edge |
| 7 (GND) | Ground Reference | Signal and power return path; must be low-impedance connection to system ground plane |
| 8–11 (Q0–Q3) | Flip-Flop Outputs | Complement of P-inputs after load, or incremented count value on each enabled clock edge |
| 12 (CLK) | Clock Input | Positive-edge-triggered; all internal state changes occur on rising edge |
| 13 (LOAD̅) | Load Enable Input | Active-low control for parallel data entry; overrides counting when asserted |
| 14 (VCC) | Power Supply | +5 V nominal supply; decoupling capacitor required within 1 cm of pin |
| 15,16 (NC) | No Connect | Not internally bonded; must remain unconnected per TI datasheet guidance |
Key Features
| Feature | Design Value |
|---|---|
| Synchronous Parallel Load | Enables immediate 4-bit value preset without disrupting clock domain timing |
| Asynchronous Clear | Guarantees deterministic zero-state initialization regardless of clock or load timing |
| Clock Enable Control | Permits dynamic gating of counting activity without external logic or clock stopping |
| TTL-Compatible I/O | Ensures interoperability with legacy 74LS, 74S, and 74F logic families in mixed-technology designs |
Applications
| Digital Test Equipment Sequencing | Industrial PLC Counter Modules |
|---|---|
Use Scenario: Generating precise step sequences for automated test fixture actuation and signal routing. IC Role / Device Role / Timing Role: Synchronous counter providing deterministic address stepping and cycle indexing. Use Value: Enables repeatable, jitter-free timing intervals with programmable start points via parallel load. | Use Scenario: Implementing discrete-event counters for machine cycle monitoring in ladder-logic controllers. IC Role / Device Role / Timing Role: Local 4-bit event accumulator interfaced to microcontroller GPIO or bus interface. Use Value: Reduces firmware overhead by offloading basic counting and reset functions from host processor. |
| Legacy Computer Bus Addressing | Protocol Analyzer State Machines |
Use Scenario: Generating memory-mapped I/O address offsets in retrocomputing expansion cards. IC Role / Device Role / Timing Role: Programmable address register with auto-increment capability during burst transfers. Use Value: Eliminates need for external address increment logic in ISA-compatible peripheral designs. | Use Scenario: Tracking protocol state transitions in hardware-accelerated serial bus analyzers. IC Role / Device Role / Timing Role: Finite-state counter managing multi-cycle command execution sequences. Use Value: Provides deterministic, glitch-free state progression synchronized to bus clock edges. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar 4-bit synchronous counter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS161N | Includes built-in carry lookahead and ripple-carry output (RCO); no parallel load enable pin - uses ENP/ENT instead | Better suited for cascaded multi-stage counters; less flexible for arbitrary presetting | Choose SN74LS161N when expanding beyond 4 bits or requiring RCO-driven chaining |
| SN74LS191N | Up/down counter with bidirectional counting mode; uses separate U/D̅ control instead of dedicated load/clear pins | Supports reversible counting but lacks true synchronous parallel load with independent clear | Choose SN74LS191N when direction flexibility outweighs need for deterministic parallel preset |
Compared with SN74LS161N and SN74LS191N, the SN74LS171D provides the most direct support for immediate 4-bit value loading and independent asynchronous reset - critical for applications requiring fast, deterministic state initialization without affecting clock domain integrity.
Availability
SN74LS171D is available at Aetrix Electronics and suitable for digital test equipment sequencing, industrial PLC counter modules, and legacy computer bus addressing requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74LS171D 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 company founded in 1930, specializing in analog and logic ICs for industrial, automotive, and communications markets.
The SN74LS171D belongs to TI's legacy 74LS logic family, designed specifically for high-reliability, medium-speed digital control systems where TTL compatibility and deterministic timing behavior are essential.
FAQ
What is the primary function of the SN74LS171D?
The SN74LS171D is a 4-bit synchronous binary counter with parallel load and asynchronous clear. It performs counting, presetting, and resetting operations on the rising edge of its clock input. Its design enables precise control of digital timing sequences in legacy and industrial systems where SN74LS171D integration is required for deterministic state management.
Does the SN74LS171D support asynchronous loading?
No, the SN74LS171D does not support asynchronous loading. Loading occurs synchronously on the rising edge of CLK when LOAD̅ is low. This ensures alignment with the system clock domain and prevents metastability. The SN74LS171D relies on this synchronous behavior for predictable timing in applications such as digital test equipment sequencing and industrial PLC counter modules.
What is the maximum operating frequency of the SN74LS171D?
The SN74LS171D has a typical propagation delay of 15 ns, supporting reliable operation up to approximately 30 MHz in ideal cascaded configurations. Actual maximum frequency depends on load capacitance, supply stability, and PCB layout. The SN74LS171D datasheet specifies timing under defined test conditions, and real-world performance should be verified with SN74LS171D in the target circuit.
Can the SN74LS171D be used in place of the SN74LS161N?
The SN74LS171D is not a drop-in replacement for the SN74LS161N due to differences in pinout, control logic, and carry generation. While both are 4-bit counters, the SN74LS161N uses enable-based counting and provides RCO for chaining, whereas the SN74LS171D emphasizes parallel load and independent clear. Substitution requires redesign of control signals and may affect SN74LS171D system timing behavior.
Is the SN74LS171D still in production by Texas Instruments?
Texas Instruments discontinued the original SN74LS171D production. However, Rochester Electronics manufactures and supplies fully compatible, tested versions using original TI die or recreated wafers approved by TI. Each SN74LS171D unit meets TI's original datasheet specifications, including timing, voltage, and functional behavior, ensuring seamless integration into legacy designs.
SN74LS171D Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Function:
- -
- Type:
- -
- Output Type:
- -
- Number of Elements:
- -
- Number of Bits per Element:
- -
- Clock Frequency:
- -
- Max Propagation Delay @ V, Max CL:
- -
- Trigger Type:
- -
- Current - Output High, Low:
- -
- Voltage - Supply:
- -
- Current - Quiescent (Iq):
- -
- Input Capacitance:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- -
- Supplier Device Package:
- -
SN74LS171D FAQ
1.How can I place an order for SN74LS171D through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS171D 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 SN74LS171D reliable?
The price and inventory of SN74LS171D are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS171D is usually 5 days.
3.What payment methods are accepted for SN74LS171D?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS171D transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS171D?
SN74LS171D orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS171D 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 SN74LS171D?
For technical support, including SN74LS171D datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS171D requirements.
6.How does Aetrix verify that SN74LS171D is sourced from the original manufacturer or authorized distributors?
All SN74LS171D 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 SN74LS171D meets industry standards.
7.What is the process for return or replacement of SN74LS171D?
All SN74LS171D units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS171D, 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 SN74LS171D part is unused and in its original packaging.
Return procedure for SN74LS171D:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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