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In response to: What microprocessors are favored for control applications?
John Schott, CAP, PE commented:
Very confusing and did not answer the question. Also skipped over the important question of opsys platform used, where PLC's rank much more stable and reliable than PAC's or PC's but lack the flexibility of communication inherent in a MS system. Embedded systems can be anything and are not a separate category. I have seen embedded systems made from standard PLC components or engineered from the ground up (reinventing the wheel). Since the brains of a controller is a large microprocessor, what is being used? (If not a proprietary chip set.) Not asking because I want to build one, but to look at capabilities. For example, PAC's and PC's use standard mP's from Intel and others that you would find in a desktop. Better PAC's may use a more robust chipset, but still using the Intel instruction set. Many questions boil down to: how stable is the processor/ operating system combination? For an aircraft autopilot, for example, a redundant processor system purpose-made for the application is a must. Nuclear power plants use a DCU system with full redundancy and fantastic stability. What happens when YOUR system crashes? RESPONSE: Sorry you didn't like the answer. I'll try again in another posting. We can't always be perfect. For now, I agree that virtually any automated control could be called an "embedded system." In practice, however, we reserve the term for a class of control systems built into devices that normally wouldn't be thought of as including automated controls, such as cellphones, dishwashers, and automobile engines. These are invariably specially designed for the application from the ground up. They are also usually space, power, and/or memory constrained.
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I’m revisiting this question because at least one reader was confused by my answer of March 24. If there’s one who commented, there must be many others who were also confused, but didn’t. So, I’ll try to clarify.
The full text of the question I was trying to answer is: “I have studied Microprocessor 8585A 8080 80 .. and all that designed since 199.. , please tell me about modern microprocessor and which are used in industrial applications nowadays.”
The bottom line is that you probably won’t use any of the conventional microprocessors designed for general-purpose computing. Either you’d be better off with a conventional packaged controller, such as a PLC, PAC, or need an embedded solution.
If you select either of the first two, you really have no choice of microprocessor — it will be whatever is in whatever you choose. Think of the unit as a black box with certain capabilities. Choose the one with the capabilities that best match your application.
Anyone planning to choose a microprocessor for a control system is ipso facto dealing with a class of controls the industry has decided to call “embedded systems.” Part of the confusion comes from thinking of “embedded system” as a kind of system, where it really is a technology. Embedded systems are, simply and not too helpfully, systems made using embedded-system technology. It’s a technology of last resort. It’s the technology we apply when constraints make it unwise or impossible to use more conventional control technology.
For example, you might want to design and build a GPS enabled autopilot for a small UAV. You’ll need a GPS receiver, drivers for the UAV’s flight control actuators, and a user interface to program flight plans through. The whole thing will have to be pulled together through a control computer. Finally, you want the whole thing to fit in the palm of your hand, so you won’t use, say, a PLC. Conventional control technology is generally just too big.
Comparing conventional industrial control technology to embedded-system technology is like comparing apples to bicycles. More accurately, it’s like comparing a bicycle to a pile of nuts and bolts, rolls of sheet metal, etc. One is the finished unit, the other is the components that go into it.
Embedded system components are very much like the things you start with to make a PLC. The difference is that components intended for embedded systems have features that make them easier to use in highly constrained applications. PLC manufacturers, for example, would likely start with off-the-shelf microprocessors. Embedded system developers typically don’t.
For example, in the UAV autopilot, you’d probably use a microcontroller rather than a microprocessor because the microcontroller includes many of the needed peripherals, such as drivers for the user interface display, and analog inputs for flight control position sensors. Some embedded microcontrollers might even include the GPS receiver. Since an autopilot really doesn’t need much computing power, the microprocessor core in the microcontroller might be an 8-bit or even 4-bit architecture. Memory would be in the IC as well, but it would be much smaller than would be considered useful in other applications.
The message I’m trying to convey is that if you really need to use embedded-system technology, your microcontroller or microprocessor choices are nearly limitless. There is no short list. During your embedded system development process, you will complile a list of features you need, then compare it to the array of microcontrollers available at the time (multiple new ones are introduced every month).
Your best introduction to embedded system development will be to attend a specialized conference, such as the Embedded Systems Conference to be held in San Jose, CA in mid-April. Similar conferences are organized at venues around the world. If you can’t make a conference, look online for a basic text on embedded systems, such as Embedded Software, published by Newnes.
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