STMicroelectronics M74HCT245B1R

Overview

M74HCT245B1R from STMicroelectronics is an octal bus transceiver with non-inverting 3-state outputs, designed for bidirectional asynchronous data bus interfacing. It features directional control (DIR), output enable (G), symmetrical drive strength (±6 mA), propagation delay of 13 ns (typ. at VCC = 4.5 V), and TTL-compatible input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V). Used in industrial backplane interfaces and legacy microcontroller bus expansion.

For engineers reviewing the M74HCT245B1R datasheet, M74HCT245B1R pinout, M74HCT245B1R application, or M74HCT245B1R equivalent, key selection criteria include bidirectional bus isolation timing, 3-state leakage under high-impedance conditions (IOZ ≤ ±10 µA), supply current efficiency (ICC ≤ 4 µA quiescent), and DIP-20 mechanical compatibility with legacy PCB footprints.

Technical Context

The M74HCT245B1R implements a silicon gate C2MOS architecture optimized for high-speed CMOS–TTL interoperability. Its DIR-controlled bidirectional path supports independent A-to-B or B-to-A data flow, while G-gated 3-state outputs provide bus isolation with tPZL/tPHZ ≤ 45 ns (max) at VCC = 4.5 V and CL = 50 pF.

Input protection circuits guard against ESD and transient overvoltage; all floating bus terminals in High-Z state must be externally biased. Propagation delays are balanced (tPLH ≅ tPHL), and output impedance is symmetrical (|IOH| = |IOL| ≥ 6 mA), enabling consistent signal integrity across both directions.

Key Specifications

Pinout & Package

Package: Plastic DIP-20 (0.300" wide), 20-pin dual in-line package with 2.54 mm pitch; compliant with JEDEC MS-001.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT245N and 74VHC245N, the M74HCT245B1R offers the widest guaranteed operating temperature range and lowest quiescent current, making it optimal for thermally constrained or mission-critical industrial deployments where timing consistency and leakage control outweigh marginal speed gains.

Availability

M74HCT245B1R is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy microcontroller bus expansion, and automotive body control modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for M74HCT245B1R 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, specializing in automotive, industrial, and power management ICs with vertical manufacturing capabilities.

The M74HCT245B1R belongs to ST's high-speed CMOS logic family, engineered for seamless TTL interoperability and robust operation in harsh industrial environments with minimal power overhead.

FAQ

What is the maximum capacitive load the M74HCT245B1R can drive reliably?

The M74HCT245B1R is characterized for CL = 50 pF and 150 pF in AC testing, with tPLH/tPHL increasing from 13 ns to 18 ns (typ.) as load rises. Driving >150 pF requires verifying setup/hold margins in-system; output rise/fall times remain <12 ns (typ.) up to 150 pF, supporting most standard PCB trace and connector capacitances.

Can the DIR and G pins be tied together for unidirectional operation?

No - DIR and G serve independent functions: DIR selects data direction (A↔B), while G enables/disables all outputs. Tying them risks undefined behavior during transitions. For unidirectional use, fix DIR at constant logic level and control bus activity solely via G, preserving correct output impedance states.

Is the M74HCT245B1R pin-compatible with older 74LS245 devices?

Yes - it uses identical DIP-20 pinout and logic function mapping, including DIR (pin 1), G (pin 19), A1–A8 (pins 2–9), B1–B8 (pins 11–18), VCC (pin 20), and GND (pin 10). No PCB changes are needed for drop-in replacement, though timing and drive improvements may require minor system timing validation.

Does the M74HCT245B1R require external pull-up or pull-down resistors on A/B bus lines?

Only during High-Z state: the datasheet explicitly states "All floating bus terminals during High Z State must be held HIGH or LOW." External biasing (e.g., 10–47 kΩ to VCC or GND) prevents indeterminate logic levels and reduces noise susceptibility on unused or tri-stated lines.