External Processor Interfaces and Operation

The way that the processor "talks" to other parts of the system is in many ways as important a factor in indicating system power as how it works internally. The processor controls the entire PC, and uses dedicated control pathways called "buses" to send information between itself and the system cache, memory and other devices. These are the processor's external interfaces, which can be different even for otherwise similar CPUs.

There are several different types of buses on a modern PC. The section on System Bus Function and Features provides the basic details on the various bus types, the hierarchy of buses, and general explanations of bus size and bandwidth. You can also find there descriptions of the I/O system buses such as PCI and ISA. At the processor level, the important buses are the processor bus and memory bus, which we discuss in more detail here.

Do the following tasks:

- Read the text.

- Broad the information in each paragraph.

- Speak of microprocessor charachteristics.

Trigonometry. Units of Measurement

by Bob Connell

 

Trigonometry is a branch of mathematics concerned with functions that describe angles. Although knowledge of trigonometry is valuable in surveying and navigation, in control systems engineering its virtue lies in the fact that trigonometric functions can be used to describe the status of objects that exhibit repeatable behavior. This includes the motion of the planets, pendulums, a mass suspended on a spring, and perhaps most relevant here, the oscillation of process variables under control.

The most common unit of measurement for angles is the degree, which is 1/360 of a whole circle.

A lesser used unit is the radian. Although the radian is not ordinarily used in angular measurement, it should be understood because when differential equations, which occur in control systems engineering, are solved, the angles emerge in radians.

On the circumference of a circle, if an arc equal in length to the radius of the circle is marked off, then the arc will subtend, at the center of the circle, an angle of 1 radian. The angle θ (or POB) in Figure 1, illustrates this.

 

 

Figure 1 - A radian defined

 

In line with this definition of a radian, the relationship between radians and degrees can be worked out. The full circumference of the circle (length 2 π r) subtends an angle of 360° at the center of the circle. An arc of length rwill subtend an angle of

 

Therefore 1 radian = 180/π deg, or π radians = 180°.

The actual value of a radian is 57°17'45", although this value is hardly ever required in control systems analysis.

If the base line OB in Figure remains fixed and the radius OP is allowed to rotate counterclockwise around the center O, then the angle 6 (or POB) increases. If the starting point for OP is coincident with OB, and OP rotates one complete rotation (or cycle) until it is again coincident with OB, then the angle 6 will be 360°. From this it is evident that 1 cycle = 360° = 2n radians.

Do the following tasks:

- Translate the text in the written form.

- Write down a summary to it.

 

Text

A microcontroller (sometimes abbreviated µC, uC or MCU) is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications.

Microcontrollers are used in automatically controlled products and devices, such as automobile engine control systems, implantable medical devices, remote controls, office machines, appliances, power tools, toys and other embedded systems. By reducing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally control even more devices and processes. Mixed signal microcontrollers are common, integrating analog components needed to control non-digital electronic systems.

Some microcontrollers may use four-bit words and operate at clock rate frequencies as low as 4kHz, for low power consumption (milliwatts or microwatts). They will generally have the ability to retain functionality while waiting for an event such as a button press or other interrupt; power consumption while sleeping (CPU clock and most peripherals off) may be just nanowatts, making many of them well suited for long lasting battery applications. Other microcontrollers may serve performance-critical roles, where they may need to act more like a digital signal processor (DSP), with higher clock speeds and power consumption.

Embedded design

A microcontroller can be considered a self-contained system with a processor, memory and peripherals and can be used as an embedded system. The majority of microcontrollers in use today are embedded in other machinery, such as automobiles, telephones, appliances, and peripherals for computer systems. While some embedded systems are very sophisticated, many have minimal requirements for memory and program length, with no operating system, and low software complexity. Typical input and output devices include switches, relays, solenoids, LEDs, small or custom LCD displays, radio frequency devices, and sensors for data such as temperature, humidity, light level etc. Embedded systems usually have no keyboard, screen, disks, printers, or other recognizable I/O devices of a personal computer, and may lack human interaction devices of any kind.

Interrupts

Microcontrollers must provide real time (predictable, though not necessarily fast) response to events in the embedded system they are controlling. When certain events occur, an interrupt system can signal the processor to suspend processing the current instruction sequence and to begin an interrupt service routine (ISR, or "interrupt handler"). The ISR will perform any processing required based on the source of the interrupt before returning to the original instruction sequence. Possible interrupt sources are device dependent, and often include events such as an internal timer overflow, completing an analog to digital conversion, a logic level change on an input such as from a button being pressed, and data received on a communication link. Where power consumption is important as in battery operated devices, interrupts may also wake a microcontroller from a low power sleep state where the processor is halted until required to do something by a peripheral event.

 

Do the following tasks:

- Read the text.

- Entitle it.

- Write down a resume to it.

Programs

Microcontroller programs must fit in the available on-chip program memory, since it would be costly to provide a system with external, expandable, memory. Compilers and assemblers are used to convert high-level language and assembler language codes into a compact machine code for storage in the microcontroller's memory. Depending on the device, the program memory may be permanent, read-only memory that can only be programmed at the factory, or program memory may be field-alterable flash or erasable read-only memory.