STMicroelectronics M74HC191B1R

Overview

M74HC191B1R from STMicroelectronics is a high-speed CMOS 4-bit synchronous up/down counter in 16-pin DIP package, operating from 2V to 6V, with 61 MHz max clock frequency (typ. at VCC = 6V), 4 µA max quiescent current at 25°C, and pin/function compatibility with standard 74-series 191 counters. It serves as a programmable counter in digital timing and control circuits, enabling precise state sequencing in industrial logic controllers.

For engineers reviewing the M74HC191B1R datasheet, M74HC191B1R pinout, M74HC191B1R application, or M74HC191B1R equivalent, key selection criteria include synchronous edge-triggered counting, asynchronous parallel load capability, MAX/MIN and Ripple Clock outputs for multi-stage carry/borrow chaining, and robust noise immunity (28% VCC min).

Technical Context

The M74HC191B1R implements a fully synchronous 4-bit binary counter using silicon gate C2MOS technology, where all state transitions occur on the LOW-to-HIGH clock edge. Its U/D control input selects counting direction, while the active-low LOAD input enables immediate parallel data loading independent of clock phase.

Carry/borrow handling is supported via dedicated active-low RC (Ripple Clock) and MAX/MIN outputs, with propagation delays tightly balanced (tPLH ≅ tPHL) and specified down to 20 ns (typ. at VCC = 6V). Input thresholds meet 28% VCC noise margin requirements across the full −55°C to +125°C operating range.

Key Specifications

Pinout & Package

Package: Plastic DIP-16 (0.300 inch width), JEDEC MS-001, body dimensions 20.0 × 8.5 mm.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 4-bit synchronous up/down counter applications.

Compared with SN74HC191N and CD74HC191E, the M74HC191B1R delivers the highest typical clock speed (61 MHz) and lowest quiescent current (4 µA), making it optimal for high-throughput, low-power industrial timing applications where timing margin and standby consumption are critical.

Availability

M74HC191B1R is available at Aetrix Electronics and suitable for industrial PLC timing modules, digital panel meter counting, and legacy system logic replacement requiring stable component supply and long-term obsolescence management.

Supply support for M74HC191B1R 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 discrete solutions with broad analog and digital portfolio coverage.

The M74HC191B1R belongs to ST's high-speed HC logic family, designed specifically for robust, low-power, wide-voltage-range digital control in harsh industrial environments.

FAQ

What is the maximum clock frequency supported by M74HC191B1R?

The M74HC191B1R achieves a typical maximum clock frequency of 61 MHz at VCC = 6V and TA = 25°C, with minimum guaranteed values of 24 MHz over the full −55°C to +125°C operating range. This specification is measured under standard AC test conditions (CL = 50 pF, input rise/fall time ≤ 6 ns).

Does M74HC191B1R support asynchronous reset?

No, the M74HC191B1R does not include a dedicated asynchronous reset input. State clearing is achieved via the active-low LOAD input combined with logic-zero data on DA–DD pins, which forces QA–QD to 0000 on the next clock edge or immediately upon LOAD assertion depending on clock state.

Can M74HC191B1R be used in 3.3V systems?

Yes - the M74HC191B1R operates reliably from 2V to 6V, including nominal 3.3V supply rails. At VCC = 3.3V, it delivers ≥25 MHz maximum clock frequency (min), 4 µA quiescent current (max), and maintains full logic-level compatibility with 3.3V CMOS interfaces.

How is carry/borrow handled across multiple M74HC191B1R devices?

Carry/borrow is implemented using the active-low RC (Ripple Clock) output, which pulses LOW on terminal count (0000 → 1111 for up, 1111 → 0000 for down). This signal drives the CLOCK input of the next stage, while ENABLE and U/D lines are shared; MA/MI provides status for overflow/underflow detection without additional gates.