Texas Instruments SN74LS348N

Overview

SN74LS348N from Texas Instruments is a TTL-compatible 8-line-to-3-line priority encoder with active-low inputs, 3-state outputs, and built-in enable control. It encodes up to eight active-low input lines (I0–I7) into three binary-weighted active-low output bits (A0–A2), supports cascading via GS and EO pins, and operates over 0°C to 70°C in PDIP-16 packaging.

For engineers reviewing the SN74LS348N datasheet, SN74LS348N pinout, SN74LS348N application, or SN74LS348N equivalent, key selection considerations include active-low encoding logic, 3-state output drive capability, propagation delay (typ. 25 ns), supply voltage range (4.75 V to 5.25 V), and compatibility with legacy LS-TTL bus systems.

Technical Context

The SN74LS348N implements priority encoding using standard bipolar TTL circuitry with Schottky-clamped transistors for speed and noise immunity. Its encoding hierarchy gives highest priority to I7 and lowest to I0, with GS (Group Select) enabling encoding only when low and EO (Enable Output) signaling valid output state.

3-state outputs are controlled by the EI (Enable Input) pin: when high, all outputs (A0–A2, GS, EO) enter high-impedance state; when low, outputs reflect encoded result or status. No internal pull-ups or latching - operation is purely combinational and level-sensitive.

Key Specifications

Pinout & Package

SN74LS348N is housed in a 16-pin plastic dual in-line package (PDIP) with 0.3-inch body width and standard DIP pin spacing (0.1 inch). Pin 1 is marked with a notch or dot; pin numbering follows counter-clockwise convention from top view.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar priority encoder applications.

Compared with SN74LS148N and 74HC148N, the SN74LS348N uniquely combines LS-TTL compatibility, active-low outputs, and integrated 3-state control in a single PDIP-16 package - making it the only option for bus-shared priority encoding in established 5 V TTL environments.

Availability

SN74LS348N is available at Aetrix Electronics and suitable for keyboard interfaces, interrupt arbiters, industrial control panels, and legacy bus address encoders requiring stable component supply and long-term obsolescence support.

Supply support for SN74LS348N 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 ICs with broad industrial and automotive reach.

The SN74LS348N belongs to TI's legacy 74LS logic family, designed specifically for reliable, low-cost, high-speed digital signal routing and encoding in commercial-grade 5 V systems.

FAQ

What is the function of the EI pin on the SN74LS348N?

The EI (Enable Input) pin on the SN74LS348N is an active-high control that places all outputs - A0, A1, A2, GS, and EO - into high-impedance state when asserted. This allows multiple SN74LS348N devices to share a common bus without contention. When EI is low, outputs reflect the encoded result or status signals. Proper decoupling near V_CC ensures stable EI response in noisy environments.

Does the SN74LS348N support cascading with other priority encoders?

Yes, the SN74LS348N supports cascading via its GS (Group Select) and EO (Enable Output) pins. GS is active-low and enables encoding; EO goes low when any input is active and GS is low. Connecting EO of one SN74LS348N to GS of another allows hierarchical priority expansion across multiple devices. Cascading preserves the fixed I7-to-I0 priority order across the entire chain.

What is the maximum propagation delay for the SN74LS348N?

The maximum propagation delay for the SN74LS348N is 25 ns under standard test conditions (V_CC = 5 V, T_A = 25°C), measured from input transition to valid output transition. This value applies to both t_PLH and t_PHL. At temperature extremes (0°C or 70°C) or supply variations, delay may increase slightly but remains within guaranteed LS-TTL timing specifications.

Can the SN74LS348N operate outside the 0°C to 70°C range?

No, the SN74LS348N is specified only for operation between 0°C and +70°C. It is a commercial-grade device and lacks characterization or qualification for extended temperature ranges. Attempting operation below 0°C or above 70°C may result in timing violations, increased propagation delay, or output instability. For industrial applications, consider redesign with temperature-rated alternatives or system-level thermal management.

Is the SN74LS348N pin-compatible with the SN74LS148N?

No, the SN74LS348N is not pin-compatible with the SN74LS148N. Although both perform 8-line-to-3-line priority encoding, their pinouts differ significantly: SN74LS348N includes an EI pin for 3-state control and places outputs differently, while SN74LS148N has no EI pin and uses active-high outputs. PCB layout and schematic must be modified to substitute one for the other.