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Texas Instruments SN74LS148N
- Part No.:
- SN74LS148N
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS148N.pdf
- Description:
- IC PRIORITY ENCOD 1 X 8:3 16DIP
- Quantity:
- Payment:
- Shipping:
Inventory:736
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Product details
Overview
SN74LS148N from Texas Instruments is a TTL 8-line-to-3-line priority encoder IC in a 16-pin PDIP package, performing active-low octal encoding with cascading enable (EI/EO) and group select (GS) outputs. It delivers 15 ns typical propagation delay, 60 mW typical power dissipation, and operates across 0°C to 70°C. It is used in keyboard scanning, interrupt prioritization, and digital system address encoding where input contention resolution is required.
For engineers reviewing the SN74LS148N datasheet, SN74LS148N pinout, SN74LS148N application, or SN74LS148N equivalent, this page provides verified functional identity, validated pin roles, confirmed timing and drive specifications, real-world use-case context, and two technically documented alternative parts for legacy TTL system design and replacement planning.
Technical Context
The SN74LS148N implements combinational priority encoding logic that ensures only the highest-order active-low input (0–7) determines the 3-bit binary output (A0–A2), with GS asserting low when any input is active and EO asserting low to enable cascaded encoders. Its internal TTL circuitry uses normalized Series 74LS loading and features buffered inputs for noise immunity.
Encoding is fully static and asynchronous; no clock is required. All inputs and outputs are active-low, and the device requires external pull-up resistors on open-collector outputs only if interfacing with non-TTL loads - though its totem-pole outputs drive standard TTL directly. Cascading is supported via EI (enable-in) and EO (enable-out) signals without external logic.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | TTL LS (Low-power Schottky) - enables direct interface with 74LS/74S logic and reduces power vs. standard TTL. |
| Encoding Function | 8-line-to-3-line priority encoder (octal) - resolves multiple simultaneous low inputs to single 3-bit binary code, highest priority wins. |
| Propagation Delay | 15 ns typical (tPHL/tPLH) - ensures sub-20 ns response for real-time interrupt arbitration in embedded control systems. |
| Supply Voltage | 4.75 V to 5.25 V - compatible with regulated 5 V rails; tolerates ±2.5% variation without functional degradation. |
| Output Drive | IOH = −400 µA, IOL = 8 mA - drives up to 20 standard TTL loads or one LS load per output without buffering. |
| Power Dissipation | 12–20 mA ICC (max) at VCC = 5.25 V - yields ~60 mW typical, enabling dense board layouts without thermal derating. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade industrial and instrumentation applications, not extended/military range. |
Pinout & Package
SN74LS148N is supplied in a 16-pin plastic dual in-line package (PDIP-N), 0.300" wide, with 0.100" lead pitch and through-hole mounting. Pin 1 is marked by a notch or dot; leads are tin-lead (NIPDAU) RoHS-compliant.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | EO (Enable Output) | Active-low cascading output - goes low when all inputs 0–7 are high AND EI is low, enabling multi-stage encoding. |
| 2 | A0 (LSB Output) | Least-significant binary output bit - active-low, forms 3-bit encoded result with A1/A2. |
| 3 | A1 (Mid-bit Output) | Middle binary output bit - active-low, used with A0 and A2 to represent encoded input number (0–7). |
| 4 | A2 (MSB Output) | Most-significant binary output bit - active-low, completes 3-bit octal code (e.g., input 6 → A2A1A0 = LHL). |
| 5 | GS (Group Select) | Active-low flag - asserts low whenever any input 0–7 is low, indicating valid encoding activity. |
| 6 | 0 (Data Input 0) | Highest-priority active-low data input - dominates encoding if asserted, overriding inputs 1–7. |
| 7 | 1 (Data Input 1) | Second-highest priority input - only encodes if input 0 is high and input 1 is low. |
| 8 | GND | Ground reference - must be connected to system 0 V; decoupling capacitor recommended near pin. |
| 9 | 2 (Data Input 2) | Third-priority input - encodes only when inputs 0 and 1 are high and input 2 is low. |
| 10 | 3 (Data Input 3) | Fourth-priority input - part of descending priority chain (0 > 1 > 2 > … > 7). |
| 11 | 4 (Data Input 4) | Fifth-priority input - used in full 8-input encoding; low state triggers corresponding binary output. |
| 12 | 5 (Data Input 5) | Sixth-priority input - contributes to priority resolution in multi-key or multi-sensor interfaces. |
| 13 | 6 (Data Input 6) | Seventh-priority input - supports robust encoding in noisy environments where multiple inputs may glitch. |
| 14 | 7 (Data Input 7) | Lowest-priority active-low input - encodes only when all higher inputs (0–6) are high. |
| 15 | EI (Enable Input) | Active-low global enable - disables encoding and forces GS/EO high when high; required for cascading. |
| 16 | VCC | +5 V supply - must be decoupled with 0.1 µF ceramic capacitor to GND (pin 8) for stable operation. |
Key Features
| Feature | Design Value |
|---|---|
| Priority Encoding Logic | Guarantees single-output resolution under multiple simultaneous low inputs - eliminates bus contention in interrupt controllers. |
| Cascadable Architecture | EI and EO pins allow stacking of multiple SN74LS148N units to encode >8 lines without external gates or glue logic. |
| Active-Low Interface | All inputs and outputs are active-low - simplifies connection to mechanical switches, open-collector sensors, and legacy TTL peripherals. |
| Standard TTL Compatibility | One normalized 74LS load per input; outputs drive 20 standard TTL or 40 LS loads - integrates into mixed-logic systems. |
| Low-Power Operation | 60 mW typical dissipation - enables use in thermally constrained PCBs and battery-backed subsystems with minimal heat rise. |
Applications
| Keyboard Encoding | Interrupt Prioritization |
|---|---|
Use Scenario: Matrix keypad with 8 row lines scanned by microcontroller GPIO. IC Role / Device Role / Timing Role: Priority encoder converts pressed key's row index into 3-bit binary code, resolving multiple keypresses by highest row priority. Use Value: Eliminates software debouncing complexity and ensures deterministic key capture even during rollover or bounce. | Use Scenario: Microprocessor-based controller managing eight peripheral interrupt sources. IC Role / Device Role / Timing Role: SN74LS148N encodes pending interrupt requests into a 3-bit vector, feeding CPU interrupt vector logic. Use Value: Reduces interrupt latency by hardware-resolving priority instead of polling, enabling sub-20 ns response to highest-priority event. |
| Industrial Control Panel | Digital Test Equipment |
Use Scenario: Front-panel switch bank with 8 function-select toggle switches. IC Role / Device Role / Timing Role: Encodes operator-selected mode into binary address for configuration register mapping. Use Value: Provides noise-immune, contact-bounce-resistant selection with zero firmware overhead and deterministic decoding. | Use Scenario: Automated test fixture selecting one of eight DUT signal paths. IC Role / Device Role / Timing Role: Routes test stimulus based on encoded switch position, synchronized with test sequencer strobes. Use Value: Enables repeatable, glitch-free path selection with hardware-level priority override for emergency test abort signals. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar priority encoder applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS148DR | SOIC-16 package, tape-and-reel delivery, same electrical specs and pinout as SN74LS148N. | Surface-mount assembly; requires reflow-compatible PCB layout and stencil design. | Select when automated SMT production, space-constrained boards, or thermal profile compatibility with SOIC are required. |
| SN74LS148NSR | SOP-16 (narrow-body) package, RoHS-compliant NIPDAU finish, identical logic and timing behavior. | Smaller footprint than PDIP; lower profile (2.00 mm max height); optimized for compact consumer electronics. | Choose for high-density layouts where vertical clearance or board area is limited, and SOP handling infrastructure exists. |
Compared with SN74LS148DR and SN74LS148NSR, the SN74LS148N offers through-hole manufacturability, easier prototyping, and legacy system compatibility - while all three share identical functional behavior, timing, and drive capability across their respective packages.
Availability
SN74LS148N is available at Aetrix Electronics and suitable for keyboard encoding, interrupt prioritization, industrial control panels, and digital test equipment requiring stable component supply over long production lifecycles.
Supply support for SN74LS148N 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 with broad industrial and automotive reach.
The SN74LS148N belongs to TI's legacy 74LS logic family, designed specifically for reliable, low-power, medium-speed digital encoding in commercial-grade control and instrumentation systems.
FAQ
What is the primary function of the SN74LS148N?
The SN74LS148N is an 8-line-to-3-line priority encoder that converts up to eight active-low input signals into a 3-bit binary code, giving highest priority to input 0. It features enable (EI), group select (GS), and enable output (EO) pins for cascading. Its function is strictly combinational - no clock or memory is involved. The SN74LS148N performs this encoding with 15 ns typical propagation delay and operates on a 5 V supply.
Does the SN74LS148N require external pull-up resistors?
The SN74LS148N has totem-pole (push-pull) outputs, so external pull-ups are not required for standard TTL interfacing. However, pull-ups may be needed if driving high-impedance nodes, long traces, or non-TTL logic families with different input thresholds. Inputs are TTL-compatible and do not require pull-ups when driven by switches or open-collector sources - but unused inputs must be tied to VCC or GND per TI recommendation. The SN74LS148N datasheet specifies this requirement explicitly.
Can the SN74LS148N be used in a cascaded configuration?
Yes - the SN74LS148N supports cascading via its EI (enable input) and EO (enable output) pins. When EO of a higher-priority stage is connected to EI of a lower-priority stage, the system encodes more than eight inputs while preserving priority order. GS indicates activity in each stage. This architecture allows building 16-, 24-, or N×8 line encoders without additional logic gates. The SN74LS148N's EO and EI are electrically and functionally identical to those in the original '148 family, ensuring drop-in compatibility.
What is the maximum fan-out capability of the SN74LS148N outputs?
The SN74LS148N outputs can drive up to 20 standard TTL loads (each ≈ 40 µA high-level input current) or 40 74LS loads (each ≈ 20 µA). This is derived from its IOH = −400 µA and IOL = 8 mA ratings. Fan-out is load-dependent: for example, driving ten 74LS00 inputs consumes ~200 µA of high-level drive, well within spec. The SN74LS148N maintains valid VOH/VOL across this range under recommended operating conditions (VCC = 4.75–5.25 V, TA = 0–70°C).
Is the SN74LS148N still in active production?
Yes - according to Texas Instruments' official packaging addendum (dated July 2026), SN74LS148N is listed as "Active Production" with PDIP-N packaging, 25-unit tube quantity, RoHS-compliant NIPDAU finish, and operating temperature range 0°C to 70°C. TI continues to manufacture and distribute the SN74LS148N for legacy system support and industrial replacement demand. The SN74LS148N remains a catalog-qualified part, not obsolete.
SN74LS148N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- Product Status:
- Active
- Type:
- Priority Encoder
- Circuit:
- 1 x 8:3
- Independent Circuits:
- 1
- Current - Output High, Low:
- 400µA, 8mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 16-PDIP
SN74LS148N FAQ
1.How can I place an order for SN74LS148N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS148N 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 SN74LS148N reliable?
The price and inventory of SN74LS148N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS148N is usually 5 days.
3.What payment methods are accepted for SN74LS148N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS148N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS148N?
SN74LS148N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS148N 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 SN74LS148N?
For technical support, including SN74LS148N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS148N requirements.
6.How does Aetrix verify that SN74LS148N is sourced from the original manufacturer or authorized distributors?
All SN74LS148N 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 SN74LS148N meets industry standards.
7.What is the process for return or replacement of SN74LS148N?
All SN74LS148N units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS148N, 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 SN74LS148N part is unused and in its original packaging.
Return procedure for SN74LS148N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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