Texas Instruments SN74ALS234N

Overview

SN74ALS234N from Texas Instruments is a 256-bit asynchronous first-in, first-out (FIFO) memory IC organized as 64 words × 4 bits, featuring 3-state outputs, data rates up to 30 MHz, and operation across 0°C to 70°C. It serves as a bit-parallel data buffer in bus-matching and rate-adaptation circuits between mismatched clock domains.

For engineers reviewing the SN74ALS234N datasheet, SN74ALS234N pinout, SN74ALS234N application, or SN74ALS234N equivalent, key selection considerations include its 30-MHz max shift-in/shift-out frequency, IR/OR status flag behavior, reset-synchronized empty/full state initialization, and compatibility with standard 5-V TTL logic families.

Technical Context

The SN74ALS234N implements a synchronous-shift-register-based FIFO architecture with independent write (on SI↑) and read (on SO↓) control paths. Its internal 62×4-bit register array supports automatic fall-through when FIFO is empty and auto-load when full-both triggered by flag-edge interactions with SI/SO.

It uses advanced low-power Schottky (ALS) technology for TTL-compatible voltage thresholds (VIH = 2 V, VIL = 0.8 V), 3-state output enable (OE), and dual status flags: IR (input-ready, active-high when space available) and OR (output-ready, active-high when valid data present).

Key Specifications

Pinout & Package

SN74ALS234N is supplied in a 20-pin plastic 300-mil DIP (N package), with pin 10 as GND and pin 20 as VCC. All pins are electrically defined per TI SDAS106B datasheet; no NC (no-connect) pins are internally bonded.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ALS234N, SN74AS234N delivers tighter timing at higher power, while 7200L15P offers CMOS efficiency but demands external control infrastructure-making SN74ALS234N optimal for plug-and-play TTL-level FIFO interfacing with minimal support components.

Availability

SN74ALS234N is available at Aetrix Electronics and suitable for UART bridging, video interface buffering, industrial PLC I/O expansion, and legacy bus protocol adaptation requiring stable component supply and long-term obsolescence management.

Supply support for SN74ALS234N 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 for industrial, automotive, and communications markets.

The SN74ALS234N belongs to TI's legacy 74ALS logic family, designed specifically for high-speed, low-power TTL-compatible FIFO buffering in mixed-clock-domain digital systems where deterministic handshaking and minimal external logic are critical.

FAQ

What is the maximum clock frequency supported by the SN74ALS234N for shift-in and shift-out operations?

The SN74ALS234N supports data rates from 0 to 30 MHz for both SI and SO inputs, as specified in the SDAS106B datasheet. This maximum frequency applies under recommended operating conditions (VCC = 4.5 V to 5.5 V, CL = 50 pF, TA = 0°C to 70°C). At 30 MHz, setup/hold and propagation timing margins remain within specification, enabling reliable high-speed buffering in real-time digital interfaces.

How does the SN74ALS234N handle empty and full FIFO conditions?

The SN74ALS234N uses two open-collector status flags: IR (input-ready) and OR (output-ready). IR goes low when the FIFO is full and remains low until SI goes low; OR goes low when the FIFO is empty and stays low until SO goes low. Both flags are asserted only when their respective conditions are met, enabling hardware handshaking without software polling. The SN74ALS234N also supports automatic fall-through (empty → immediate output) and auto-load (full → immediate input) modes based on SI/SO flag interaction.

Is the SN74ALS234N pin-compatible with other 74-series FIFO devices like the SN74ALS233N?

No, the SN74ALS234N is not pin-compatible with SN74ALS233N. The SN74ALS233N is a 128-bit (32×4) FIFO with different pin assignments-including separate clock inputs for write and read-and lacks the IR/OR status flags found on the SN74ALS234N. The SN74ALS234N's 20-pin N-package layout, including dedicated SI/SO, IR/OR, and RST pins, is unique to its 256-bit implementation and cannot be substituted without PCB redesign.

What is the role of the RST (reset) input on the SN74ALS234N, and how must it be used at power-up?

The RST input on the SN74ALS234N is an active-low asynchronous master reset that must be pulsed low after power-up to initialize the FIFO to a known empty state. This action sets IR high, OR low, and all Q outputs low. Failure to apply RST results in undefined flag states and unpredictable output behavior. The datasheet specifies a minimum RST pulse width of 15 ns at VCC = 4.5 V to 5.5 V, and the SN74ALS234N remains in reset until RST returns high.

Does the SN74ALS234N support 3-state output control, and how is it implemented?

Yes, the SN74ALS234N supports 3-state output control via the OE (output-enable) pin. When OE is high, the Q0–Q3 outputs enter high-impedance state regardless of FIFO content or OR flag status. When OE is low, Q0–Q3 drive valid data corresponding to the current FIFO output word. OE does not affect IR or OR flag operation, allowing independent control of data bus contention and status monitoring. This feature enables shared-bus architectures where multiple devices drive the same data lines.