Texas Instruments SN74ALS29854NT

Overview

SN74ALS29854NT from Texas Instruments is an 8-bit to 9-bit parity bus transceiver with integrated odd-parity generation and checking, open-collector ERR flag output, latch-enable (LE) and clear (CLR) control, and dual-directional A↔B data flow. It operates at 4.75–5.25 V, supports 0°C to 70°C ambient, and delivers 8 ns propagation delay (A/B ↔ B/A, CL = 50 pF). It is used in legacy industrial backplanes and memory subsystems requiring real-time parity error detection and diagnostic flag storage.

For engineers reviewing the SN74ALS29854NT datasheet, SN74ALS29854NT pinout, SN74ALS29854NT application, or SN74ALS29854NT equivalent, key selection considerations include its 24-pin PDIP (NT) package, open-collector ERR output drive capability (IOL = 48 mA), inverted-parity mode for system diagnostics, latch-controlled error flag retention, and compatibility with ALS logic voltage thresholds (VIH = 2 V, VIL = 0.8 V).

Technical Context

The SN74ALS29854NT implements a synchronous, bidirectional 8-bit bus transceiver with dedicated 9th-bit parity path. Its internal parity generator computes odd parity across A1–A8 inputs and outputs it on PARITY; during reverse transfer (B→A), it checks B1–B8 plus incoming PARITY and asserts ERR if mismatched. The ERR signal is edge-sensitive and can be latched via LE or cleared asynchronously via CLR.

Control logic supports four primary modes: A→B with parity generation, B→A with parity checking, isolation (both OEA/OEB high), and A→B with forced inverted parity (both OEA/OEB low). All I/Os are TTL-compatible with ALS-level input thresholds and 3-state outputs except ERR, which is open-collector and rated for 5.5 V sink.

Key Specifications

Pinout & Package

SN74ALS29854NT is supplied in a 24-pin plastic dual-in-line package (PDIP), NT suffix, 300-mil width, with 0.100″ lead pitch and through-hole mounting. Pin 1 is top-left corner (notch-up orientation).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-bit parity transceiver applications.

Compared with SN74ALS29854NT, SN74AS29854N offers higher speed at the cost of increased power and noise sensitivity, while AM29854PC provides identical functionality with slightly tighter DC specs and long-standing qualification in defense systems - making it ideal for BOM refresh without redesign.

Availability

SN74ALS29854NT is available at Aetrix Electronics and suitable for industrial backplane bus, memory subsystem interface, legacy test equipment bus, and digital signal processing chassis applications requiring stable component supply and long-term obsolescence management.

Supply support for SN74ALS29854NT 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 company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74ALS29854NT belongs to TI's legacy 74ALS logic family, designed specifically for high-reliability, medium-speed bus interfacing in commercial-temperature industrial systems with strict parity integrity requirements.

FAQ

What is the function of the PARITY pin on the SN74ALS29854NT?

The PARITY pin on the SN74ALS29854NT serves as a bidirectional 9th-bit interface: it outputs odd parity of A1–A8 during A→B transfers and acts as the parity input for B→A parity checking. When enabled for B→A operation, the device compares the value on PARITY against the computed odd parity of B1–B8 and asserts ERR if they differ. This dual-role design eliminates separate parity lines and reduces bus width overhead.

Can the SN74ALS29854NT operate with a 3.3 V supply?

No, the SN74ALS29854NT is specified only for 4.75 V to 5.25 V operation per its recommended conditions and absolute maximum ratings. Applying 3.3 V will result in undefined logic states, failure to meet VIH/VIL thresholds, and unreliable parity generation or checking. For 3.3 V systems, consider modern alternatives like SN74LVC8T245 with external parity logic or dedicated 3.3 V parity ICs.

How does the inverted-parity mode work on the SN74ALS29854NT?

Inverted-parity mode activates when both OEA and OEB are low, causing the SN74ALS29854NT to generate even parity instead of odd parity during A→B transfers. This creates a deliberate parity mismatch on the B bus, forcing ERR assertion during subsequent B→A parity checks. It is used exclusively for system diagnostics - verifying error-detection paths without injecting actual data corruption.

Is the ERR output of the SN74ALS29854NT compatible with 3.3 V logic inputs?

Yes, the ERR output is open-collector and rated for up to 5.5 V, so it can safely interface with 3.3 V logic inputs when pulled up to 3.3 V via an external resistor. The SN74ALS29854NT itself does not drive ERR high; the external pull-up determines the logic-high voltage level, enabling direct connection to 3.3 V microcontrollers or FPGAs without level shifters.

What is the purpose of the LE and CLR pins on the SN74ALS29854NT?

The LE (latch-enable) pin captures the instantaneous state of ERR on its rising edge and holds it in an internal register until cleared; CLR (clear) asynchronously resets that register, forcing ERR high. Together, they enable diagnostic flag persistence across bus idle periods or clock domain boundaries - critical for firmware that polls ERR infrequently or during low-power states. Both functions are fully documented in the SN74ALS29854NT function table and error-flag waveforms.