SN74HC4020DT

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The SN74HC4020DT is a precision monolithic synchronous binary up/down counter which has two independent binary up/down counters in a single package. The counters feature separate up/down control (U/D), cascade control (A/B) and clear (CLR) inputs. The down count inputs (with B perpendicular A) and the terminal count outputs (Q15) and the carry out (COUT) are provided for cascading operations.

This device offers significant advantages over the standard combination of asynchronous counters and clock dividers in terms of size, speed and power. The up/down controls allow easy counting in both directions while the cascade inputs provide flexibility and synchronization, allowing counters of any length to be created. The three-state outputs also make it an ideal choice for multiplexers or other devices which require buffering.

Working Principle

The SN74HC4020DT utilizes two internal 4-bit synchronous binary counters implemented with positive edge-triggered D-type flip-flop stages. The device is triggered by the positive edge of the U/D, A/B and CLR inputs, which respectively clock the up/down counter, initiate cascading operations, and clear all the stage outputs. The presence of an active high-to-low transition on the U/D, A/B and CLR inputs is necessary for any clock and terminal count operations to occur.

Whenever one of the three inputs are active, the SN74HC4020DT will initiate the parallel loading of data from the data inputs (D3, D2, D1, D0) through the 7408 logic gates. The newly loaded data will remain at the output until it is clocked by one of the three clock inputs, causing the Q outputs to advance. Depending on the logic state of the A/B input, the Q and Q* outputs will be connected to either the up counter or the down counter, and the following operations will then take place:

• When the U/D input is active low, data loads on the rising edge and the Q outputs advance up to Q15;
• When the U/D input is active high, data loads on the rising edges and the Q outputs move down to Q0;
• When the A/B input is active, data loads on the rising edges and the Q and Q* outputs move in opposite directions, toggling off at the intermediate Q15 and Q0 conditions.

The Carry Output (COUT) also becomes active whenever an overflow/underflow condition occurs, as well as at QCEC (Q/Q* equal condition). The COUT will remain active for a couple of clock cycles before it is reset. This ensures that the COUT will remain active on subsequent cycles of the U/D input.

Applications

Due to its small size and high speed, the SN74HC4020DT is ideal for applications that require precise timing and minimal power consumption. It has been used in a wide range of applications, such as processor clocking, pulse generation, clock pulse synchronization, as well as in data acquisition, control systems, instrumentation, and automotive systems.

The SN74HC4020DT has also been used as a divide-by-n counter, providing divisible input clock frequencies suitable for applications such as pulse-width modulation, frequency division, and rate generation. The counters can also be used in multiplexers or other devices which require buffering of signals.

The SN74HC4020DT is widely used in programmable logic controllers (PLCs) and embedded microcontrollers, due to its ability to be integrated into high-speed CPU design easily. The device is highly reliable, and it is also RoHS-compliant, making it suitable for many industrial and commercial applications.

In summary, the SN74HC4020DT is a highly efficient, high-speed, and reliable integrated circuit for counting and dividing applications. Its small size and low power consumption make it an ideal choice for a wide variety of applications, including data acquisition, instrumentation, control systems, and PLCs. It is also RoHS-compliant and is suitable for high-speed CPU designs.

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