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Logic - Multivibrators

The CD74HCT4538M is an 8-stage binary ripple counter and an 8-bit resetable synchronous binary up/down counter contained in one package. This device has a two stage synchronous presettable counter, with counter stages programmable as either a divide-by-2N or a divide-by-N/2 magnitude multivibrator. It contains 24 edges sensitive combinatorial inputs and 10 outputs. A few of its common applications are frequency divisions, counting and time measurement.

Application Field

The device is used in various applications such as frequency division, time measurement, and counting. In frequency division circuits, the counter output provides a divided down logic output frequency. The logic output frequency can be half or one fourth of the frequency of the incoming clock. Since the counter has 8 fixed outputs, the output logic frequency can only be 1/8, 1/4, 1/2, and 1 of the frequency of the incoming clock.

It is also useful in time measurement applications where the input is a clock pulse stream, and the frequency of the pulses needs to be divided down manually, or preset before hand to achieve the required output. Other applications include application in industrial control, process control and medical instrumentation.

Working Principle

The CD74HCT4538M counter works by counting the number of input clock pulses. The frequency of the outgoing pulse depends on the number of clock pulses that are counted. The device is particularly important in applications that require the incoming frequency to be divided down to a smaller and more manageable frequency.

The device consists of two main counters. The divider by 2N counter has two clock inputs that are controlled by the two input voltage levels. They are called CLK0 and CLK1. The first is used to clock in a single input pulse and the second is used to reset the counter. The divider by N/2 counter is a two stage counter, divided by two bit stages that divide the incoming pulse by 4. The two main counters can be programmed in a variety of ways to get the required output pulse.

The device can be programmed to count from 0 to 255. It can reset itself after reaching the maximum count and start counting from 0 again. When the counter is reset, all output pins become logic low for one clock period and then logic high for one clock period, thus enabling external logic to distinguish the reset and non-reset states of the counter. The device can be set to count up or down, depending on the application requirements.

In summary, the CD74HCT4538M is an 8-stage binary ripple counter and an 8-bit resetable synchronous binary up/down counter. The two main counters can be programmed in a variety of ways to get the desired output pulse, thus making it useful in frequency divisions, counting, and time measurement applications.

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