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Texas Instruments SN74LS348DR
- Part No.:
- SN74LS348DR
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74LS348DR.pdf
- Description:
- IC PRIORITY ENCOD 1 X 8:3 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,945
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Product details
Overview
SN74LS348DR from Texas Instruments is an 8-line to 3-line priority encoder with active-low inputs, 3-state outputs, and TTL-compatible logic levels. It encodes up to eight active-low input lines (I0–I7) into three binary-coded outputs (Y0–Y2), includes enable (EI) and group-select (GS) control, and operates over 0°C to 70°C. It is used in keyboard encoding, interrupt request prioritization, and address encoding in legacy industrial control systems.
For engineers reviewing the SN74LS348DR datasheet, SN74LS348DR pinout, SN74LS348DR application, or SN74LS348DR equivalent, key selection criteria include active-low input polarity, 3-state output drive capability, propagation delay (typ. 25 ns), supply voltage range (4.75 V to 5.25 V), and compatibility with standard LS-TTL logic families.
Technical Context
The SN74LS348DR implements a priority-encoding function where the highest-order active-low input determines the output code, overriding lower-priority inputs. Its internal logic includes NAND/NOR gates and inverters configured for strict priority resolution and simultaneous generation of the group-select (GS) flag when any input is active.
It features dual-control enables: EI (Enable Input) must be low to activate encoding, and GS (Group Select) goes low only when at least one input is asserted - both signals are active-low and TTL-compatible. The 3-state outputs are disabled when EI is high, presenting high-impedance states to prevent bus contention.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | LS-TTL: ensures compatibility with 74LS-series devices and defined noise margins (0.8 V VIH min, 2.0 V VOH min) |
| Input Configuration | 8 active-low inputs (I0–I7): supports direct connection to open-collector switches or pull-up resistor networks |
| Output Type | 3-state active-low outputs (Y0–Y2, GS): enables shared-bus operation without external tri-state buffers |
| Propagation Delay | 25 ns max (tPLH/tPHL at VCC = 5 V, TA = 25°C): defines worst-case timing for synchronous system integration |
| Supply Voltage | 4.75 V to 5.25 V: requires regulated +5 V rail; out-of-range operation risks logic instability or damage |
| Operating Temperature | 0°C to +70°C: validated for commercial-grade environments, not extended or military temperature ranges |
| Output Drive | IOL = 8 mA / IOH = –0.4 mA (at VCC = 5 V): supports fan-out of up to 20 LS-TTL loads per output |
Pinout & Package
SN74LS348DR is supplied in a 16-pin SOIC (D) package with standard 1.27 mm pitch, 7.5 mm body width, and JEDEC MS-012AC outline. Pin assignments follow TI's standardized 74LS348 layout.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| I0–I7 | Active-low data inputs | Priority-encoded inputs; I7 has highest priority, I0 lowest; all internally pulled high via ~10 kΩ resistors in typical test conditions |
| Y0–Y2 | Active-low encoded outputs | Binary output (Y2 Y1 Y0) representing highest-priority asserted input; high-impedance when EI = high |
| EI | Enable input | Active-low global enable; disables all outputs (3-state) and deactivates encoding when high |
| GS | Group select output | Active-low flag indicating "any input active"; remains high only when all I0–I7 are inactive |
| VCC | Positive supply | +5 V power pin; requires local 0.1 µF ceramic decoupling adjacent to pin |
| GND | Ground reference | Signal and power ground return; must be low-impedance connection to minimize switching noise |
Key Features
| Feature | Design Value |
|---|---|
| Priority encoding logic | Guarantees deterministic output when multiple inputs assert simultaneously - critical for interrupt arbitration |
| 3-state outputs with common enable | Allows direct connection to shared data buses without external bus transceivers or isolation logic |
| Active-low input/output architecture | Matches legacy switch-matrix designs using pull-up resistors and mechanical contacts |
| LS-TTL compatible voltage thresholds | Ensures interoperability with 74LS, 74S, and 74F families without level-shifting circuitry |
| Group-select (GS) status flag | Provides immediate system-level awareness of encoder activity without polling individual inputs |
Applications
| Keyboard Scan Interface | Interrupt Priority Arbiter |
|---|---|
Use Scenario: Matrix keyboard with 8 rows scanned sequentially via microcontroller port lines. IC Role / Device Role / Timing Role: SN74LS348DR encodes pressed row into 3-bit binary code and asserts GS to signal interrupt to CPU. Use Value: Reduces software polling overhead and eliminates ambiguity when multiple keys are pressed concurrently. | Use Scenario: Microprocessor-based controller managing eight peripheral interrupt sources with fixed priority. IC Role / Device Role / Timing Role: SN74LS348DR maps highest-priority pending interrupt to CPU vector address lines and triggers IRQ line via GS. Use Value: Enables hardware-resolved priority without dedicated priority encoder ICs or complex firmware state machines. |
| Address Line Encoder | Legacy Bus Status Monitor |
Use Scenario: Industrial PLC backplane with 8-slot expansion where slot ID must be derived from presence detection. IC Role / Device Role / Timing Role: SN74LS348DR converts slot-present signals (active-low) into 3-bit slot address for configuration register mapping. Use Value: Provides deterministic, zero-latency addressing for hot-plug detection in non-PCI bus architectures. | Use Scenario: Diagnostic subsystem monitoring 8 fault indicators (e.g., overtemp, overcurrent, watchdog timeout) on a single board. IC Role / Device Role / Timing Role: SN74LS348DR compresses fault status into encoded output and pulses GS to latch fault condition in diagnostic register. Use Value: Minimizes I/O pin usage while preserving fault hierarchy for root-cause analysis in field service tools. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar priority encoding applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS148N | Same 8-to-3 priority encoder function but with active-high enable (EI) and active-high outputs (A0–A2); no GS output | Lacks group-select flag; requires external logic to detect any-input-active condition | Choose SN74LS148N only if system design uses active-high signaling and can synthesize GS externally |
| 74HC148PW | CMOS version with wider VCC range (2 V to 6 V), lower power, but incompatible input thresholds (VIH = 3.5 V min at VCC = 5 V) | Not directly interchangeable with LS-TTL due to input sensitivity; requires level-shifting or redesign | Select 74HC148PW only in new designs targeting low-power operation and full 5 V CMOS compatibility |
Compared with SN74LS148N and 74HC148PW, the SN74LS348DR uniquely provides active-low outputs plus a dedicated GS flag in a drop-in LS-TTL package - essential for maintaining signal polarity and simplifying interrupt-handling logic in legacy systems.
Availability
SN74LS348DR is available at Aetrix Electronics and suitable for keyboard interface design, interrupt management in industrial controllers, and address encoding in legacy embedded systems requiring stable component supply and long-term obsolescence support.
Supply support for SN74LS348DR 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 SN74LS348DR belongs to TI's legacy 74LS logic family, designed specifically for reliable, low-cost digital encoding in commercial-grade control and instrumentation systems of the 1970s–1990s.
FAQ
What is the function of the GS pin on the SN74LS348DR?
The GS (Group Select) pin on the SN74LS348DR is an active-low output that goes low whenever any of the eight inputs (I0–I7) is asserted. It serves as a system-level activity flag, enabling microcontrollers or other logic to detect encoder activation without scanning individual inputs. This behavior is intrinsic to the SN74LS348DR design and differs from alternatives like SN74LS148N, which lacks GS.
Is the SN74LS348DR pin-compatible with the SN74LS148N?
No, the SN74LS348DR is not pin-compatible with the SN74LS148N. Although both are 8-to-3 priority encoders, they differ in pin assignment: SN74LS348DR places GS on pin 14 and uses pins 1–8 for I0–I7, while SN74LS148N assigns EI to pin 1 and outputs to pins 4–6. Direct replacement would require PCB redesign and signal re-routing.
What is the maximum clock or data rate supported by the SN74LS348DR?
The SN74LS348DR does not operate on a clock signal - it is combinational logic. Its speed is defined by propagation delay: tPLH and tPHL are 25 ns maximum at VCC = 5 V and TA = 25°C. This supports reliable operation in systems with input transition rates below ~20 MHz, assuming proper setup/hold timing for upstream drivers.
Can the SN74LS348DR drive LEDs directly?
The SN74LS348DR outputs can sink up to 8 mA per pin (IOL), sufficient to drive small indicator LEDs with appropriate current-limiting resistors (e.g., 330 Ω for ~10 mA at 5 V). However, because outputs are active-low, LEDs must be connected anode-to-VCC and cathode-to-output. Do not exceed 8 mA per output or 50 mA total package current to avoid exceeding absolute maximum ratings.
Does the SN74LS348DR require external pull-up resistors on its inputs?
External pull-ups are recommended but not strictly required for the SN74LS348DR inputs. Internal weak pull-ups (~10 kΩ typical) exist in most LS-TTL devices, but their strength varies with process and temperature. For robust noise immunity and guaranteed high-state definition - especially in noisy industrial environments - 4.7 kΩ to 10 kΩ external pull-ups to VCC are standard practice per TI application guidance for SN74LS348DR.
SN74LS348DR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Type:
- Priority Encoder
- Circuit:
- 1 x 8:3
- Independent Circuits:
- 1
- Current - Output High, Low:
- 400µA, 24mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74LS348DR FAQ
1.How can I place an order for SN74LS348DR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS348DR 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 SN74LS348DR reliable?
The price and inventory of SN74LS348DR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS348DR is usually 5 days.
3.What payment methods are accepted for SN74LS348DR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS348DR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS348DR?
SN74LS348DR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS348DR 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 SN74LS348DR?
For technical support, including SN74LS348DR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS348DR requirements.
6.How does Aetrix verify that SN74LS348DR is sourced from the original manufacturer or authorized distributors?
All SN74LS348DR 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 SN74LS348DR meets industry standards.
7.What is the process for return or replacement of SN74LS348DR?
All SN74LS348DR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS348DR, 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 SN74LS348DR part is unused and in its original packaging.
Return procedure for SN74LS348DR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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