Texas Instruments SN74ALS235N

Overview

SN74ALS235N from Texas Instruments is a 64-word × 5-bit asynchronous first-in, first-out (FIFO) memory IC using advanced low-power Schottky IMPACT™ technology. It supports data rates up to 25 MHz, features 3-state outputs, and operates across 0°C to 70°C. It is used in data buffering between mismatched-speed digital subsystems such as UART-to-processor interfaces.

For engineers reviewing the SN74ALS235N datasheet, SN74ALS235N pinout, SN74ALS235N application, or SN74ALS235N equivalent, key selection criteria include FIFO depth (64 words), word width (5 bits), asynchronous SI/SO control timing, flag behavior (OR/IR/AF-AE/HF), and DIP-20 package compatibility with legacy TTL systems.

Technical Context

The SN74ALS235N implements a bit-parallel, word-oriented FIFO with independent write (SI rising edge) and read (SO falling edge) clocks. Its internal 65×5-bit register array enables fall-through operation when empty and automatic shift-in when full, controlled by IR and OR status flags.

Flag logic generates AF/AE (active at ≤8 or ≥56 words), HF (high at ≥32 words), and synchronized OR/IR pulses tied directly to SI/SO transitions. All outputs are noninverting, and OE disables Q0–Q4 only - status flags remain active regardless of OE state.

Key Specifications

Pinout & Package

SN74ALS235N uses a 20-pin plastic dual in-line package (DIP), 300-mil width, with standard through-hole mounting and 0.1-inch pin pitch.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar FIFO memory applications.

Compared with SN74ALS235N, SN74AS235N delivers tighter timing at higher current draw, while 7205L15 offers CMOS efficiency and wider word width but mandates layout changes and interface adaptation - making SN74ALS235N optimal for TTL-native, cost-sensitive, or legacy-replacement use cases.

Availability

SN74ALS235N is available at Aetrix Electronics and suitable for UART bridging, video synchronization, industrial PLC I/O expansion, and legacy bus protocol translation requiring stable component supply and long-term obsolescence support.

Supply support for SN74ALS235N 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 SN74ALS235N belongs to TI's 74ALS logic family, designed specifically for high-speed, low-power TTL-compatible memory and interface functions in commercial-grade digital systems.

FAQ

What is the exact memory depth and word width of the SN74ALS235N?

The SN74ALS235N implements a 64-word × 5-bit FIFO, totaling 320 bits of storage. Each word is loaded or read in parallel across D0–D4 and Q0–Q4. This configuration supports precise word-aligned buffering where 5-bit control fields or status vectors must be preserved intact without splitting or reassembly.

How does the SN74ALS235N handle empty and full conditions during data transfer?

When the SN74ALS235N FIFO is empty and SI goes low, input data falls through directly to Q0–Q4 - generating an OR pulse indicating immediate validity. When full, holding SI high and pulsing SO low triggers automatic shift-in, causing IR to pulse high. Neither condition causes data loss: additional SI pulses are ignored when full; additional SO pulses are ignored when empty.

Which pins on the SN74ALS235N control output enable and master reset, and what are their active states?

Pin 1 (OE) is the active-low output enable controlling Q0–Q4 tri-state behavior; when high, outputs enter high-impedance mode. Pin 20 (RST) is the active-low master reset that clears the FIFO, forces Q0–Q4 low, sets IR high, and sets OR low. Both require clean, debounced low-level pulses for reliable operation.

Can the SN74ALS235N operate with mixed 3.3-V and 5-V logic interfaces?

No - the SN74ALS235N is strictly a 5-V device with VIH = 2.0 V and VIL = 0.8 V, designed for TTL/ALS logic families. Driving its inputs from 3.3-V logic may result in marginal or invalid recognition of high levels; similarly, its 24-mA sink outputs exceed 3.3-V I/O voltage ratings. Level-shifting circuitry is required for interoperability.

What are the timing-critical parameters for synchronizing SI and SO operations in the SN74ALS235N?

Critical timing parameters for the SN74ALS235N include tsu = 0 ns (data setup before SI↑), th = 17 ns (data hold after SI↑), and tw(SI/SO) = 15 ns (minimum pulse width). For SO-triggered reads, tpd(SO↓→Q) = 4–22 ns defines output validity window. These values ensure robust operation across the full 0–25 MHz range under worst-case temperature and voltage conditions.