Texas Instruments SN74HC148N

Overview

SN74HC148N from Texas Instruments is an 8-line to 3-line priority encoder IC in PDIP-16 package, performing active-low octal-to-binary encoding with cascading enable (EI/EO) and group-select (GS) outputs. It operates from 2V to 6V, delivers ±4 mA output drive at 5V, and achieves typical propagation delay of 38 ns at 6V. It is used in keyboard encoders, interrupt prioritization, and digital control panels where input contention resolution is required.

For engineers reviewing the SN74HC148N datasheet, SN74HC148N pinout, SN74HC148N application, or SN74HC148N equivalent, key selection considerations include its active-low input/output logic, cascading capability via EI/EO, guaranteed 10 LSTTL load drive, low 80-μA max ICC supply current, and compatibility with standard HC logic families across industrial temperature range (–40°C to +85°C).

Technical Context

The SN74HC148N implements combinational priority encoding with fixed 8-input (I0–I7), 3-output (A0–A2) binary mapping and three control signals: EI (enable input), EO (enable output), and GS (group select). All inputs and outputs are active-low, and encoding follows strict priority order - only the highest-priority asserted input determines the output code.

Its functional modes are fully defined by the truth table: when EI is high, all outputs are forced high (inactive); when EI is low, the lowest-numbered active input (e.g., I0 > I1 > … > I7) drives A2–A0 to its corresponding 3-bit binary complement, while EO goes low if any input is active and GS goes low only when at least one input is active.

Key Specifications

Pinout & Package

SN74HC148N is housed in a 16-pin plastic dual in-line package (PDIP), measuring 19.31 mm × 6.35 mm, with 0.1-inch lead pitch and through-hole mounting. The package is RoHS-compliant with NiPdAu lead finish and rated for industrial temperature operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS148N, SN74HC148N offers wider voltage range, lower power, and RoHS compliance but slightly longer propagation delay; compared with CD74HC148E, it shares full functional equivalence but differs solely in PDIP packaging for manual assembly and socket compatibility.

Availability

SN74HC148N is available at Aetrix Electronics and suitable for industrial control panels, keyboard encoders, interrupt arbiters, and digital signal routing selectors requiring stable component supply across extended product lifecycles.

Supply support for SN74HC148N 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 leader delivering analog, embedded processing, and logic solutions with emphasis on reliability, scalability, and long-term support.

The SN74HC148N belongs to TI's classic 74HC logic family, designed specifically for robust, low-power combinational logic functions in industrial, automotive, and communications infrastructure applications.

FAQ

What is the logic polarity of inputs and outputs on the SN74HC148N?

The SN74HC148N uses active-low logic throughout: all eight data inputs (I0–I7), the enable input (EI), and all three encoded outputs (A0–A2), plus EO and GS, are asserted low. This means a logic '0' activates the function - for example, I0 = 0 encodes to A2A1A0 = 111, and EI = 1 disables encoding entirely. This polarity simplifies connection to open-collector sensors or pushbutton switches with pull-up resistors.

Can multiple SN74HC148N devices be cascaded to handle more than eight inputs?

Yes, the SN74HC148N supports seamless cascading using its EI and EO pins. Connect EO of a higher-priority stage to EI of the next stage; when the first stage detects any active input, its EO goes low, enabling the second stage. This allows building 16-, 24-, or N×8-input priority encoders without external logic. The GS output of each stage indicates whether that stage contributed to the final encoded result.

What is the maximum clock or data rate supported by the SN74HC148N?

The SN74HC148N is a purely combinational device with no internal clock - its speed is governed by propagation delay. At VCC = 6 V, tpd is 38 ns max (A0–A2 or EO), supporting reliable operation up to ~13 MHz in systems where setup/hold margins permit. For clean edge-sensitive sampling, ensure input transitions settle before downstream latching; use the GS signal as a valid-data strobe to avoid glitches during input transients.

Does the SN74HC148N require external pull-up or pull-down resistors on its inputs?

Yes - all unused inputs of the SN74HC148N must be tied to a defined logic level (VCC or GND) to prevent floating states that cause excessive current draw or erratic output behavior. TI recommends connecting unused data inputs (e.g., I0–I7) to VCC via 10-kΩ pull-ups, and EI should be pulled high if not actively controlled. Leaving inputs unconnected violates recommended operating conditions and risks device malfunction.

Is the SN74HC148N compatible with 3.3V microcontroller GPIOs?

Yes, the SN74HC148N is fully compatible with 3.3V systems: its VIH(min) is 2.0 V at VCC = 3.3 V, and its VOL(max) is 0.33 V at IOL = 4 mA - well within 3.3V logic thresholds. It can be powered from 3.3V and directly driven by and drive 3.3V CMOS outputs. Ensure VCC is decoupled with a 0.1-μF ceramic capacitor placed near pin 16 to maintain noise immunity.