NXP 74HC590D: An 8-Bit Binary Counter with Output Register and Asynchronous Reset

The NXP 74HC590D is a high-speed silicon-gate CMOS device that serves as a versatile and efficient 8-bit binary counter. This integrated circuit is designed to count clock pulses and store the result, making it a fundamental component in numerous digital systems, from simple event counters to complex state machines and timing applications.

A key architectural feature of the 74HC590D is its internal structure, which separates the counting function from the output stage. The device contains an 8-bit ripple binary counter that advances on the low-to-high transition of the clock (CP) input. Crucially, the counted value is not immediately presented to the output pins. Instead, it is held in an internal latch. This value is then transferred to the 8-bit output register upon a low-to-high transition of the Register Clock (RCK) input. This separation provides significant functional advantages. It allows the counting operation to continue uninterrupted, even while the stored value is being read or output to a bus, effectively eliminating glitches on the output lines during counting.

Another critical feature is its asynchronous reset function. The Master Reset (MR) input, when held high, immediately and asynchronously clears the entire counter to zero, independent of the state of the clock signals. This provides designers with immediate control to initialize the count value at any moment, which is essential for system startup or error recovery scenarios.

The device also includes a Output Enable (OE) pin. When OE is set to a low logic level, the outputs are enabled and display the data stored in the output register. When OE is high, the outputs are forced into a high-impedance state. This tri-state capability allows the 74HC590D to be connected directly to a microprocessor bus or to other devices in a shared bus architecture without risking data contention.

Furthermore, the 74HC590D offers a ripple carry output (RCO). This pin goes low when the counter reaches its maximum count (255) and rolls over to zero, acting as a carry-out signal. This output can be easily cascaded to the clock input of a subsequent 74HC590D, enabling the design of counters with 16, 24, or more bits with minimal additional circuitry.

In summary, the 74HC590D combines counting, latching, and tri-state output control into a single package. Its robust design, characterized by a separate output register and an immediate reset function, ensures stable and flexible operation in a wide array of digital logic designs.

ICGOODFIND: The NXP 74HC590D is an exceptionally useful IC for designing glitch-free counting systems. Its integrated output register and tri-state outputs make it ideal for bus-oriented applications, while the asynchronous reset provides reliable and immediate initialization.

Keywords: 8-Bit Binary Counter, Output Register, Asynchronous Reset, Tri-State Outputs, Ripple Carry Output.