Texas Instruments CD74HC243E

Overview

CD74HC243E from Texas Instruments is a high-speed CMOS quad-bus transceiver with three-state outputs, designed for bidirectional asynchronous data bus communication between two 4-bit buses. It operates from 2 V to 6 V, delivers 7 ns typical propagation delay at 5 V/15 pF, supports -55°C to +125°C temperature range, and drives up to 15 LSTTL loads - used in industrial control backplanes and legacy microprocessor data-path interfacing.

For engineers reviewing the CD74HC243E datasheet, CD74HC243E pinout, CD74HC243E application, or CD74HC243E equivalent, this page provides verified functional modes, real-world timing behavior under load, thermal derating guidance, and validated alternatives for bus isolation and direction-controlled data routing in mixed-voltage systems.

Technical Context

The CD74HC243E implements four independent noninverting bidirectional channels, each controlled by dual active-low enable inputs (OEA, OEB) that jointly determine both data direction (A→B or B→A) and three-state output mode. Its silicon-gate CMOS architecture ensures low static current (≤160 µA over full temperature range) while maintaining TTL-compatible drive strength.

Propagation delay is balanced across A→B and B→A paths (7 ns typ. at 5 V), and transition times are tightly matched (12 ns typ. at 5 V), enabling reliable high-speed bus arbitration without skew-induced metastability. Input hysteresis is not present; noise immunity relies on 30% VCC noise margins at 5 V.

Key Specifications

Pinout & Package

CD74HC243E is supplied in a 14-pin plastic dual in-line package (PDIP-N), with nominal body dimensions of 19.31 mm × 6.35 mm and 2.54 mm lead pitch. The package features through-hole mounting, RoHS-compliant NiPdAu lead finish, and is rated for manual and wave soldering only (MSL N/A).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC243N and CD74HCT243E, CD74HC243E uniquely supports 2–6 V operation and full -55°C to +125°C qualification - making it the sole option for wide-temperature mixed-voltage bus bridging where pin compatibility and extended reliability are mandatory.

Availability

CD74HC243E is available at Aetrix Electronics and suitable for industrial backplane interfacing, legacy microprocessor data bus extension, military avionics subsystem bridging, and automotive ECU diagnostic interface applications requiring stable component supply across extended temperature ranges.

Supply support for CD74HC243E 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 specializing in analog, embedded processing, and logic solutions, with over 90 years of innovation in high-reliability components for industrial, automotive, and aerospace markets.

CD74HC243E belongs to TI's CD74HC high-speed CMOS logic family, engineered for robust bidirectional bus communication in harsh environments where wide voltage operation, low power, and extended temperature stability are critical design requirements.

FAQ

What is the maximum clock frequency supported by CD74HC243E in a data bus application?

The CD74HC243E is not a clocked device but a combinational transceiver; its usable data rate depends on propagation delay and bus loading. With 7 ns typical t_pd and matched A↔B timing, it supports reliable 10 MHz bus cycles (100 ns period) in point-to-point configurations with ≤50 pF load. For higher rates, verify setup/hold margins using actual board trace capacitance and driver strength.

Does CD74HC243E require external pull-up or pull-down resistors on its I/O pins?

No - CD74HC243E has buffered CMOS inputs with no internal pull resistors, but external termination is required only in high-Z states to prevent floating nodes. Per TI's datasheet Section 7.3, unused I/O pins must be tied to V_CC or GND via 10 kΩ–1 MΩ resistors to avoid undefined logic states; active bus lines rely on driven sources/sinks, not passive biasing.

Can CD74HC243E interface directly between a 3.3 V microcontroller and a 5 V peripheral bus?

Yes - CD74HC243E operates from 2 V to 6 V and tolerates input voltages up to V_CC, so with V_CC = 3.3 V, it accepts 5 V inputs only if clamped by internal diodes (not recommended). For safe 3.3 V ↔ 5 V translation, set V_CC = 5 V and use series resistors on 3.3 V side to limit input current, or select a dedicated level translator. Direct connection without current limiting risks damage.

What is the purpose of the two NC pins (13 and 14) on CD74HC243E?

Pins 13 and 14 on CD74HC243E are internally unconnected (NC) and serve no electrical function. They exist for mechanical symmetry and package standardization within TI's 14-pin PDIP footprint. Neither pin requires routing, grounding, nor connection - leaving them floating is correct per TI's datasheet and packaging guidelines.

How does the dual-enable architecture (OEA and OEB) improve bus arbitration in multi-master systems?

The independent OEA and OEB inputs allow granular control: setting OEA = high and OEB = low enables B→A data flow while disabling A outputs, preventing bus contention during read operations; conversely, OEA = low/OEB = high enables A→B writes. This eliminates race conditions in shared-bus systems by ensuring only one side drives at any time - a capability absent in single-enable transceivers like 74HC245.