Texas Instruments SN74HC148DRE4

Overview

SN74HC148DRE4 from Texas Instruments is an 8-line to 3-line priority encoder IC with active-low inputs and outputs, operating across 2V–6V supply range. It features cascading enable (EI/EO) signals, 16ns typical propagation delay at 4.5V, ±4-mA output drive, and low 80-μA max ICC. It encodes eight data lines into 3-bit binary (4-2-1 octal) for interrupt prioritization in microcontroller I/O expansion systems.

For engineers reviewing the SN74HC148DRE4 datasheet, SN74HC148DRE4 pinout, SN74HC148DRE4 application, or SN74HC148DRE4 equivalent, key selection criteria include its priority encoding logic, active-low signal compatibility, SOIC-16 package footprint, cascading capability for multi-stage encoding, and guaranteed operation from –40°C to +85°C.

Technical Context

The SN74HC148DRE4 implements combinational priority encoding where only the highest-order asserted (low) input determines the 3-bit binary output (A2–A0), while GS (Group Select) and EO (Enable Output) support hierarchical chaining of multiple encoders without external logic. Its truth table defines strict priority order: input 7 > 6 > … > 0.

All inputs and outputs are active-low; EI must be low to enable encoding, and EO goes low when EI is low and all inputs are high-enabling daisy-chaining. Propagation delays vary with VCC: 38ns max at 6V, 45ns at 4.5V, and 225ns at 2V (CL = 50 pF).

Key Specifications

Pinout & Package

SN74HC148DRE4 is housed in a 16-pin SOIC (D) package measuring 9.90 mm × 3.90 mm with 1.27 mm pitch, RoHS-compliant NiPdAu lead finish, and moisture sensitivity level 1 (260°C peak reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC148DRE4, SN74LS148N trades power efficiency and voltage flexibility for raw speed in legacy 5V environments, while 74HC148PW offers identical functionality in a smaller package - demanding tighter layout controls but delivering significant area savings.

Availability

SN74HC148DRE4 is available at Aetrix Electronics and suitable for industrial PLC I/O expansion, microcontroller interrupt prioritization, keypad scan matrix compression, and legacy system bus address encoding requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN74HC148DRE4 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 specializing in analog, embedded processing, and logic solutions, with decades of heritage in industry-standard logic families including 74HC, 74AHC, and 74LVC.

SN74HC148DRE4 belongs to TI's 74HC high-speed CMOS logic portfolio, engineered for low-power, wide-supply-voltage operation in industrial control, instrumentation, and interface consolidation applications.

FAQ

What is the function of the GS (Group Select) pin on the SN74HC148DRE4?

The GS (Group Select) pin on the SN74HC148DRE4 is an active-low output that goes LOW whenever any of the eight inputs (I0–I7) is asserted (LOW), indicating that at least one valid request is present. In the SN74HC148DRE4, GS serves as a ready/interrupt flag - it remains HIGH only when all inputs are HIGH (i.e., no requests), making it ideal for triggering MCU interrupts or enabling downstream logic. This behavior is defined in the device's function table and verified across all operating conditions.

Can SN74HC148DRE4 operate reliably at 3.3V supply voltage?

Yes, SN74HC148DRE4 operates reliably at 3.3V supply voltage, as confirmed by TI's Recommended Operating Conditions: VCC min = 2V, nominal = 5V, max = 6V. At 3.3V, input thresholds are VIH ≥ 2.31V and VIL ≤ 0.99V (30%/70% of VCC), ensuring clean logic discrimination. Propagation delay increases to ~55ns (typical), and output drive remains sufficient for 3.3V LVTTL loads - all parameters are fully characterized and guaranteed in the official datasheet for SN74HC148DRE4.

How does cascading work with SN74HC148DRE4 using EI and EO pins?

Cascading with SN74HC148DRE4 uses EI (Enable Input) and EO (Enable Output) to build N-input priority encoders. The EO of a lower-priority stage connects to the EI of the next higher-priority stage. When the first SN74HC148DRE4 has all inputs HIGH, its EO goes LOW, enabling the second SN74HC148DRE4 to respond to its inputs - effectively extending priority hierarchy. This architecture requires no external gates and is validated in TI's application diagrams for 16-bit encoding, ensuring deterministic behavior across temperature and voltage for SN74HC148DRE4.

Is SN74HC148DRE4 pin-compatible with older 74LS148 encoders?

No, SN74HC148DRE4 is not pin-compatible with 74LS148. Although both are 16-pin DIP/SOIC encoders with identical pin numbering (e.g., I0–I7 on pins 2–9, A0–A2 on 11–13), the SN74HC148DRE4 uses SOIC (D) package with 1.27 mm pitch, while legacy 74LS148 often uses PDIP (N) or CDIP (J) with 2.54 mm pitch. More critically, electrical behavior differs: SN74HC148DRE4 has CMOS input structure (high impedance, rail-to-rail thresholds), whereas 74LS148 uses bipolar TTL inputs - direct substitution risks logic-level incompatibility and excessive loading.

What is the maximum clock frequency or data rate supported by SN74HC148DRE4?

SN74HC148DRE4 is a combinational logic device with no internal clock; its effective "data rate" depends on input transition speed and propagation delay. With 38 ns max tpd at 6V (CL = 50 pF), it supports input assertion/deassertion rates up to ~10 MHz for reliable encoding - assuming clean edges and proper termination. The datasheet specifies input transition time limits (e.g., 400 ns max at 6V), and TI confirms SN74HC148DRE4 performance under these conditions in switching characteristics tables. No maximum frequency rating is specified because it is asynchronous.