STMicroelectronics M74HC166B1R

Overview

M74HC166B1R from STMicroelectronics is a high-speed CMOS 8-bit parallel-in/serial-out (PISO) shift register with silicon gate C2MOS technology, operating from 2V to 6V supply, delivering 63 MHz max clock frequency (typ.) at VCC = 6V, 4 mA minimum output drive, and asynchronous active-low clear. It enables synchronous parallel loading or serial shifting via SHIFT/LOAD control and is used in digital logic interfacing, microcontroller I/O expansion, and serial data conversion circuits.

For engineers reviewing the M74HC166B1R datasheet, M74HC166B1R pinout, M74HC166B1R application, or M74HC166B1R equivalent, key selection factors include its PISO architecture, edge-triggered clock (LOW-to-HIGH), active-low asynchronous CLEAR and SHIFT/LOAD control, and DIP-16 package compatibility with legacy 74-series designs.

Technical Context

The M74HC166B1R implements an 8-stage D-type flip-flop chain with dual-path input selection: parallel data (A–H) loaded synchronously on the rising clock edge when SHIFT/LOAD is low, or serial data (SI) shifted right on each rising clock edge when SHIFT/LOAD is high. Clock enable (CLOCK INH) is active-low and must be held high only while CLOCK is high.

Its asynchronous CLEAR overrides all inputs-including clock-and forces all Q outputs low. Input protection includes ESD and transient voltage suppression. Propagation delays are balanced (tPLH ≅ tPHL), and noise immunity meets VNIH/VNIL ≥ 28% VCC across the full temperature range (–55°C to +125°C).

Key Specifications

Pinout & Package

Package: Plastic DIP-16 (0.300″ wide), JEDEC MS-001, body dimensions 20.0 mm × 6.9 mm × 3.3 mm.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PISO shift register applications.

Compared with SN74HC165PWR and CD74HC165M96, the M74HC166B1R uniquely offers CLOCK INH for precise clock gating, –55°C to +125°C qualification, and DIP-16 compatibility-making it optimal for legacy upgrades and thermally demanding industrial control.

Availability

M74HC166B1R is available at Aetrix Electronics and suitable for microcontroller I/O expansion, industrial serial data conversion, and legacy system bus bridging requiring stable component supply and long-term DIP-16 availability.

Supply support for M74HC166B1R 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 and broad IP portfolio.

The M74HC166B1R belongs to ST's high-speed HC logic family, designed specifically for drop-in replacement of legacy 74-series logic in industrial control, instrumentation, and embedded systems requiring extended temperature operation and low static power.

FAQ

Can M74HC166B1R operate at 3.3 V?

Yes. The device is fully specified from VCC = 2 V to 6 V, including 3.3 V. At 3.3 V, VIH = 2.31 V (70% VCC), VIL = 0.99 V (30% VCC), and fMAX ≈ 40 MHz (typ.), making it compatible with standard 3.3 V CMOS logic families without level shifters.

What happens if CLOCK INH is toggled asynchronously?

Toggling CLOCK INH while CLOCK is low may cause metastability or missed clock edges. The datasheet specifies that CLOCK INH must be changed to HIGH only while CLOCK is held HIGH to ensure glitch-free clock inhibition and avoid unintended register updates.

Is the CLEAR input truly asynchronous and immune to clock glitches?

Yes. CLEAR is a dedicated asynchronous active-low input that forces all flip-flops to zero regardless of CLOCK state, SHIFT/LOAD level, or data inputs. Its propagation delay to QH is guaranteed ≤ 35 ns (max) at VCC = 6 V, and it overrides all other signals without dependency on clock edges.

Does M74HC166B1R support hot insertion or live insertion?

No. The device lacks hot-swap protection circuitry such as power-up sequencing control or I/O clamp diodes rated for live insertion. Its absolute maximum rating for VI is –0.5 V to VCC + 0.5 V, and applying signals before VCC stabilization risks latch-up or permanent damage.