Texas Instruments SN74LS243DR

Overview

SN74LS243DR from Texas Instruments is a quadruple bus transceiver IC designed for asynchronous two-way data communication between parallel buses in TTL-level systems. It features dual-directional data flow (A↔B), hysteresis (~400 mV) at inputs for noise immunity, PNP input structure to reduce DC loading, and supports terminated line driving down to 133 Ω. It operates across 0°C to 70°C and is used in industrial control backplanes and legacy computing interconnects.

For engineers reviewing the SN74LS243DR datasheet, SN74LS243DR pinout, SN74LS243DR application, or SN74LS243DR equivalent, key selection considerations include direction control logic (GAB/GBA), output drive capability (±24 mA), propagation delay (12–18 ns), and SOIC-14 package compatibility with legacy TTL board layouts.

Technical Context

The SN74LS243DR implements four independent bidirectional data channels, each controlled by separate enable signals GAB (A-to-B) and GBA (B-to-A). Its logic diagram confirms positive-logic operation with active-low isolation and latch modes when opposing enables are asserted.

Input hysteresis improves noise margin in electrically noisy environments, while PNP input stages minimize current draw from upstream drivers. Output stages deliver ±24 mA sink/source capability under VCC = 5 V, enabling direct interface with 50 Ω–133 Ω terminated lines without external buffers.

Key Specifications

Pinout & Package

SN74LS243DR is housed in a 14-pin SOIC (D) package, 3.9 mm wide, 1.75 mm max height, with 1.27 mm pitch and RoHS-compliant NiPdAu lead finish. Moisture sensitivity level is Level-1, unlimited reflow profile.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar bus transceiver applications.

Compared with SN74LS244N and SN74LS245N, the SN74LS243DR offers unique per-transceiver direction control and latch functionality-critical for fault-tolerant bus arbitration and legacy system emulation where fine-grained isolation is required.

Availability

SN74LS243DR is available at Aetrix Electronics and suitable for industrial backplane interconnects, legacy computer bus extensions, programmable logic interfaces, and microcontroller peripheral bridges requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74LS243DR 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 founded in 1930, delivering analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74LS243DR belongs to TI's legacy 74LS logic family, engineered specifically for robust, low-power TTL-compatible bus interfacing in mission-critical industrial and computing infrastructure.

FAQ

What is the function of GAB and GBA pins on the SN74LS243DR?

The GAB (Gate A→B) and GBA (Gate B→A) pins are active-low enables that independently control data direction per transceiver channel. When GAB is low and GBA is high, data flows from A1–A4 to B1–B4; when GBA is low and GAB is high, data flows from B1–B4 to A1–A4. Both high yields isolation; both low latches A = B. This dual-enable architecture enables precise bus arbitration in the SN74LS243DR.

Does the SN74LS243DR support hot-swapping or live insertion?

The SN74LS243DR does not include built-in hot-swap protection such as power-on reset, slew-rate control, or undervoltage lockout. However, its high-impedance isolation mode (GAB = GBA = HIGH) allows safe insertion into a powered bus if external current-limiting and sequencing are implemented. Always verify bus voltage stability before insertion, as the SN74LS243DR has no internal clamping beyond absolute maximum ratings.

Can the SN74LS243DR drive a 50 Ω transmission line?

No-the SN74LS243DR is characterized to drive terminated lines down to 133 Ω, not 50 Ω. Driving a 50 Ω load would exceed its ±24 mA output rating under typical VCC = 5 V conditions, risking excessive power dissipation and potential output stage degradation. For 50 Ω systems, use a dedicated line driver or buffer stage downstream of the SN74LS243DR.

What is the significance of hysteresis in the SN74LS243DR inputs?

The ~400 mV hysteresis on all SN74LS243DR inputs increases noise immunity by creating distinct high-to-low and low-to-high switching thresholds. This prevents multiple toggles during slow or noisy signal transitions-especially valuable on shared, unterminated, or long-trace buses where ringing or ground bounce may occur. It directly enhances reliability in electrically harsh environments where the SN74LS243DR is deployed.

Is the SN74LS243DR pin-compatible with newer CMOS logic families like 74HC or 74AHC?

No-the SN74LS243DR is not pin-compatible with 74HC243 or 74AHC243 due to differing pin assignments: the HC/AHC variants use DIR and OE pins instead of GAB/GBA, and their pinouts allocate different functions to pins 1, 2, 12, and 13. While functional equivalents exist, PCB redesign is required to substitute the SN74LS243DR with CMOS versions, as the SN74LS243DR's SOIC-14 footprint does not map to those parts' signal allocations.