STMicroelectronics M74HC299B1R

Overview

M74HC299B1R from STMicroelectronics is a high-speed CMOS 8-bit parallel-in/parallel-out (PIPO) shift register with asynchronous clear, 3-state bus-compatible I/O, and four operational modes (HOLD, SHIFT LEFT, SHIFT RIGHT, LOAD). It operates from 2V to 6V, delivers 80MHz max clock frequency at 6V, supports dual serial outputs (QA'–QH'), and features independent 3-state enable (G1/G2) for bidirectional bus interfacing in microcontroller peripheral expansion systems.

For engineers reviewing the M74HC299B1R datasheet, M74HC299B1R pinout, M74HC299B1R application, or M74HC299B1R equivalent, key selection criteria include asynchronous reset timing (tPHL ≤ 45ns @6V), symmetrical drive strength (6mA min IOH/IOL on QA–QH), high noise immunity (28% VCC), wide temperature range (–55°C to +125°C), and DIP-20 package compatibility with legacy 74-series layouts.

Technical Context

The M74HC299 implements a synchronous edge-triggered (rising-clock) 8-bit shift register with fully independent mode control via S0/S1 inputs and dual 3-state enables (G1, G2 active-low). Its asynchronous CLEAR input overrides all modes and resets Qn outputs independently of clock phase.

It integrates two distinct output banks: QA–QH provide 6mA min drive with 3-state control for parallel bus driving; QA'–QH' deliver 4mA min standard outputs optimized for serial chaining. Input protection includes ESD diodes and transient voltage clamping per IEC 61000-4-2 Level 4.

Key Specifications

Pinout & Package

Package: Plastic DIP-20 (0.300" width), 2.54mm pitch, JEDEC MS-001 compliant. RoHS-compliant lead finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC299N and 74VHC299N, the M74HC299B1R offers superior extended-temperature support (–55°C to +125°C), tighter propagation delay consistency, and broader supply tolerance (up to 6V), making it optimal for ruggedized embedded systems where reliability across environmental extremes is critical.

Availability

M74HC299B1R is available at Aetrix Electronics and suitable for microcontroller peripheral expansion, industrial PLC I/O multiplexing, legacy system bus interface, and test equipment signal routing requiring stable component supply across extended temperature and voltage ranges.

Supply support for M74HC299B1R 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, designing and manufacturing analog, digital, and mixed-signal ICs for automotive, industrial, and power management applications.

The M74HC299 belongs to ST's high-speed CMOS logic family, engineered for drop-in replacement of bipolar 74-series devices while delivering lower power, higher noise immunity, and extended temperature operation in industrial control and instrumentation systems.

FAQ

What is the maximum clock frequency supported by M74HC299B1R at 3.3V supply?

At VCC = 3.3V, the M74HC299B1R supports a maximum clock frequency of 24MHz (min) per AC specifications. This is derived from the fMAX parameter table: at 4.5V it is 24MHz min over –40°C to +85°C, and at 2.0V it drops to 4.8MHz min. Interpolation confirms 3.3V operation falls within the 12–24MHz range, with typical performance near 18MHz.

Can M74HC299B1R operate with mixed voltage interfaces (e.g., 3.3V logic driving its inputs while VCC = 5V)?

Yes - the M74HC299B1R accepts input voltages from 0V to VCC, so 3.3V logic signals are fully compatible when VCC = 5V. VIH(min) is 3.15V at VCC = 4.5V and 4.2V at VCC = 6V, meaning 3.3V inputs meet VIH requirements only if VCC ≤ 4.5V. For 5V VCC, a level shifter or resistor divider is required to ensure VIH ≥ 4.2V.

How does the asynchronous CLEAR interact with ongoing shift operations?

The CLEAR input has absolute priority: when asserted (LOW), it forces all Qn outputs to LOW immediately, overriding any active SHIFT, LOAD, or HOLD operation - even mid-cycle. Propagation delay from CLEAR to QA' is 18ns (typ) at 6V, and the register remains reset until CLEAR is deasserted, after which normal mode operation resumes on the next clock edge.

Are QA–QH and QA'–QH' outputs electrically isolated when G1/G2 are HIGH?

No - asserting G1 or G2 HIGH places only QA–QH into high-impedance state; QA'–QH' remain active and driven regardless of G1/G2 status. This design allows continuous monitoring of internal register contents (via QA'–QH') while isolating the parallel bus (QA–QH), enabling real-time diagnostics without disrupting data flow.