Microcontroller Topics

• analog to digital conversion
• input output devices
• internal timer
• clock frequencies
• power sleep
• logic level
• cpu clock
• battery applications
• mike barr
• analog to digital
• power consumption
• program memory
• service routine
• milliwatts
• button press
• performance applications
• microcontrollers
• communication link
• typical applications

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Microcontroller, Microcontroller

Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a, typically small, read/write memory. "Embedded Systems Dictionary" by Jack Ganssle and Mike Barr, p.173 Microcontrollers are designed for small applications. Thus, in contrast to the microprocessors used in personal computers and other high-performance applications, simplicity is emphasized. Some microcontrollers may operate at clock frequencies as low as 32kHz, as this is adequate for many typical applications, enabling 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.

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.

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). 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.

This allows a part to be used in a wider variety of applications than if pins had dedicated functions. Microcontrollers have proved to be highly popular in embedded systems since their introduction in the 1970s.

The microcontroller vendors often trade operating frequencies and system design flexibility against time-to-market requirements from their customers and overall lower system cost. Manufacturers have to balance the need to minimize the chip size against additional functionality.

A microcontroller instruction set usually has many instructions intended for bit-wise operations to make control programs more compact.

According to Semico, Over 4 billion 8-bit microcontrollers were sold in 2006. http://www.semico.com A typical home in a developed country is likely to have only four general-purpose microprocessors but around three dozen microcontrollers. A typical mid range automobile has as many as 30 or more microcontrollers. They can also be found in any electrical device: washing machines, microwave ovens, telephones etc. 18F8720 microcontroller in an 80-pin TQFP package.

These languages are either designed specially for the purpose, or versions of general purpose languages such as the C programming language. Compilers for general purpose languages will typically have some restrictions as well as enhancements to better support the unique characteristics of microcontrollers. Some microcontrollers have environments to aid developing certain types of applications. Microcontroller vendors often make tools freely available to make it easier to adopt their hardware.

For example, BASIC on the early microcontrollers Intel 8052 "8052-Basic Microcontrollers" by Jan Axelson 1994 ; BASIC and FORTH on the Zilog Z8 "Optimizing the Zilog Z8 Forth Microcontroller for Rapid Prototyping"by Robert Edwards 1987, page 3.http://www.ornl.gov/info/reports/1987/3445602791343.pdf as well as some modern devices.Typically these interpreters support interactive programming.

These allow a developer to analyze what the behavior of the microcontroller and their program should be if they were using the actual part. A simulator will show the internal processor state and also that of the outputs, as well as allowing input signals to be generated. While on the one hand most simulators will be limited from being unable to simulate much other hardware in a system, they can exercise conditions that may otherwise be hard to reproduce at will in the physical implementation, and can be the quickest way to debug and analyze problems.

Source: Wikipedia > Microcontroller