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An inside look at industrial Ethernet communication protocols

Pulse Width Modulation (PWM) uses digital signals to control power applications, as well as being fairly easy to convert back to analog with a minimum of hardware. Analog systems, such as linear power supplies, tend to generate a lot of heat since they are basically variable resistors carrying a lot of current. Digital systems don’t generally generate as much heat. Almost all the heat generated by a switching device

A principal consideration for industrial control networks, where the monitoring and control of real-life processes must often occur quickly and at set times, is the guaranteed maximum communication time from one node to another. If you’re controlling the position of a nuclear reactor coolant valve with a digital network, you need to be able to guarantee that the valve’s network node will receive the proper positioning signals from

Shift registers, like counters, are a form of sequential logic. Sequential logic, unlike combinational logic is not only affected by the present inputs, but also, by the prior history. In other words, sequential logic remembers past events. Shift registers produce a discrete delay of a digital signal or waveform. A waveform synchronized to a clock, a repeating square wave, is delayed by “n” discrete clock times, where “n” is the

PARTS AND MATERIALS Four 6 volt batteries One capacitor, 100 µF electrolytic, 35 WVDC (Radio Shack catalog # 272-1028 or equivalent) One capacitor, 0.1 µF, non-polarized (Radio Shack catalog # 272-135) One 555 timer IC (Radio Shack catalog # 276-1723) Dual operational amplifier, model 1458 recommended (Radio Shack catalog # 276-038) One NPN power transistor—(Radio Shack catalog # 276-2041 or equivalent) Three 1N4001 rectifying diodes (Radio Shack catalog # 276-1101) One 10 kΩ potentiometer, linear taper (Radio Shack catalog # 271-1715) One 33 kΩ

A decoder is a circuit that changes a code into a set of signals. It is called a decoder because it does the reverse of encoding, but we will begin our study of encoders and decoders with decoders because they are simpler to design. A common type of decoder is the line decoder which takes an n-digit binary number and decodes it into 2n data lines. The simplest is the

Perhaps the most challenging aspect of interpreting ladder diagrams, for people more familiar with electronic schematic diagrams, is how electromechanical relays are represented. Compare these two equivalent diagrams: First, the ladder diagram: Next, the schematic diagram: Based on your observations of these two diagrams, explain how electromechanical relays are represented differently between ladder and schematic diagrams.

PARTS AND MATERIALS Three batteries, each one with a different voltage Three equal-value resistors, between 10 kΩ and 47 kΩ each When selecting resistors, measure each one with an ohmmeter and choose three that are the closest in value to each other. Precision is very important for this experiment! CROSS-REFERENCES Lessons In Electric Circuits, Volume 1, chapter 10: “DC Network Analysis” LEARNING OBJECTIVES How a resistor network can function as a voltage signal averager

We can subtract one binary number from another by using the standard techniques adapted for decimal numbers (subtraction of each bit pair, right to left, “borrowing” as needed from bits to the left). However, if we can leverage the already familiar (and easier) technique of binary addition to subtract, that would be better. As we just learned, we can represent negative binary numbers by using the “two’s complement” method

One caveat with signed binary numbers is that of overflow, where the answer to an addition or subtraction problem exceeds the magnitude which can be represented with the alloted number of bits. Remember that the place of the sign bit is fixed from the beginning of the problem. With the last example problem, we used five binary bits to represent the magnitude of the number, and the left-most (sixth) bit

With addition being easily accomplished, we can perform the operation of subtraction with the same technique simply by making one of the numbers negative. For example, the subtraction problem of 7 - 5 is essentially the same as the addition problem 7 + (-5). Since we already know how to represent positive numbers in binary, all we need to know now is how to represent their negative counterparts and we’ll be able to

The “vocabulary” of instructions which any particular microprocessor chip possesses is specific to that model of chip. An Intel 80386, for example, uses a completely different set of binary codes than a Motorola 68020, for designating equivalent functions. Unfortunately, there are no standards in place for microprocessor instructions. This makes programming at the very lowest level very confusing and specialized. When a human programmer develops a set of instructions to directly tell

A synchronous counter, in contrast to an asynchronous counter, is one whose output bits change state simultaneously, with no ripple. The only way we can build such a counter circuit from J-K flip-flops is to connect all the clock inputs together, so that each and every flip-flop receives the exact same clock pulse at the exact same time: Now, the question is, what do we do with the J and

Before the advent of solid-state logic circuits, logical control systems were designed and built exclusively around electromechanical relays. Relays are far from obsolete in modern design, but have been replaced in many of their former roles as logic-level control devices, relegated most often to those applications demanding high current and/or high voltage switching. Systems and processes requiring “on/off” control abound in modern commerce and industry, but such control

Adding binary numbers is a very simple task, and very similar to the longhand addition of decimal numbers. As with decimal numbers, you start by adding the bits (digits) one column, or place weight, at a time, from right to left. Unlike decimal addition, there is little to memorize in the way of rules for the addition of binary bits: 0 + 0 = 0 1 + 0 = 1 0 + 1 = 1 1 + 1 = 10 1 + 1 + 1 = 11 Just as with decimal addition, when the sum in one

Having learned about digital memory devices in the last chapter, we know that it is possible to store binary data within solid-state devices. Those storage “cells” within solid-state memory devices are easily addressed by driving the “address” lines of the device with the proper binary value(s). Suppose we had a ROM memory circuit written, or programmed, with certain data, such that the address lines of the ROM served as