Texas Instruments SN74ALS29818NT

Overview

SN74ALS29818NT from Texas Instruments is a high-speed 8-bit parallel pipeline register with serial shadow register (right-shift only), performing parallel-to-serial and serial-to-parallel conversion in write control store and diagnostic applications. It operates at 5 V, features 24-pin PDIP packaging, 0°C to 70°C temperature range, and 215 mW typical power dissipation.

For engineers reviewing the SN74ALS29818NT datasheet, SN74ALS29818NT pinout, SN74ALS29818NT application, or SN74ALS29818NT equivalent, key selection considerations include its dual-register architecture (pipeline + serial shadow), OEY-controlled 3-state Y outputs, SRCLK/ORCLK dual-clock operation, and functional equivalence to AMD AM29818 for legacy system replacement.

Technical Context

The SN74ALS29818NT implements a two-stage register architecture: an 8-bit pipeline register loaded in parallel from DQ0–DQ7 or the shadow register, and an 8-bit serial shadow register loaded serially via SDI or from Y0–Y7 or the pipeline register. Its MODE and OEY inputs configure data flow direction and output enable state.

Operation relies on two independent clocks: SRCLK controls shadow register shifting and loading, while ORCLK governs pipeline register loading and Y-output latching. The OEY input enables/disables Y0–Y7 outputs without affecting internal register states, supporting bus-sharing in multi-device systems.

Key Specifications

Pinout & Package

SN74ALS29818NT uses a 24-pin plastic dual in-line package (PDIP), designated NT by Texas Instruments. Pin numbering follows standard DIP convention with Pin 1 at top-left corner when notch is oriented upward.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-bit pipeline register applications.

Compared with SN74ALS29818NT, SN74ALS819DW adds parity monitoring but removes Y-output control-limiting bus arbitration capability-while AM29818PC offers identical functionality as a verified second source, preserving timing, pinout, and application behavior without design change.

Availability

SN74ALS29818NT is available at Aetrix Electronics and suitable for write control store implementation, serial diagnostic subsystems, and legacy industrial controller repair requiring stable component supply across extended production lifecycles.

Supply support for SN74ALS29818NT 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 SN74ALS29818NT belongs to TI's legacy ALS logic family, designed specifically for high-reliability, medium-speed digital control applications including CPU microcode storage, diagnostic shadow registers, and programmable logic interface staging.

FAQ

What is the primary function of the SN74ALS29818NT in a digital system?

The SN74ALS29818NT functions as an 8-bit parallel pipeline register with integrated serial shadow register, enabling simultaneous parallel data staging and serial diagnostic access. It performs parallel-to-serial and serial-to-parallel conversion, making it essential in write control store architectures and embedded self-test systems. Its dual-clock (SRCLK/ORCLK) and OEY-controlled outputs allow flexible data routing without bus contention, a core capability of the SN74ALS29818NT.

Does the SN74ALS29818NT support bidirectional data flow on the DQ0–DQ7 pins?

Yes, the DQ0–DQ7 pins on the SN74ALS29818NT serve as a bidirectional I/O port: they accept parallel data for loading the pipeline or shadow register and reflect registered values when configured as outputs. However, outputs are disabled when OEY is high, and external bus drivers must manage directionality-SN74ALS29818NT itself does not auto-sense direction. This behavior is explicitly defined in the function table for the SN74ALS29818NT.

How does the OEY pin affect the Y0–Y7 outputs of the SN74ALS29818NT?

The OEY pin on the SN74ALS29818NT is an active-low output enable that places Y0–Y7 in high-impedance state when high, and drives registered data when low. Unlike general-purpose 3-state buffers, OEY does not affect internal register operation-shadow and pipeline registers continue updating per SRCLK/ORCLK regardless of OEY state. This decoupling allows safe bus sharing and is a defining feature of the SN74ALS29818NT's architecture.

Is the SN74ALS29818NT pin-compatible with the SN74ALS819?

No, the SN74ALS29818NT is not pin-compatible with the SN74ALS819. While both are 24-pin ALS devices, SN74ALS29818NT uses Pin 1 for OEY and Pins 15–22 for Y0–Y7, whereas SN74ALS819 assigns Pin 1 to PE (parity output) and Pins 15–22 to Y0–Y7 but lacks OEY entirely-instead using Pin 13 for SDO and omitting OEY functionality. Their pinouts differ in critical control signal assignments, so direct substitution requires PCB modification.

What is the maximum clock frequency supported by the SN74ALS29818NT for SRCLK and ORCLK?

The SN74ALS29818NT does not specify a maximum clock frequency directly, but minimum pulse widths define practical limits: SRCLK high/low time ≥25 ns (40 MHz max theoretical), ORCLK high/low time ≥15 ns (67 MHz max theoretical). Propagation delays (e.g., 12–25 ns SRCLK→SDO) and setup/hold times (e.g., tsu(SDI)=10 ns) further constrain reliable operation. For robust timing closure, designs targeting ≤25 MHz SRCLK and ≤33 MHz ORCLK align with published AC characteristics of the SN74ALS29818NT.