Microcontrollers (MCU) are complete computer systems on a chip. They combine an arithmetic logic unit (ALU), memory, timer/counters, serial port, input/output (I/O) ports and a clock oscillator. Most microcontrollers include a 4-bit, 8-bit, 16-bit, 32-bit, 64-bit, or 128-bit data bus. The number of serial channels and I/O ports varies among devices. Serial interfaces include controller area network (CAN), inter-integrated circuit (I²C), serial peripheral interface (SPI), serial communications interface (SCI), universal serial bus (USB), universal asynchronous receiver transmitter (UART), and universal synchronous/asynchronous receiver transmitter (USART). Common features include watchdog timers, direct memory access (DMA) channels, pulse width modulation (PWM) channels, power saving modes, oscillator safeguards (OSG), low frequency auxiliary oscillators (LFAO), low voltage detectors (LVD), readout protection, and liquid crystal display (LCD) drivers. Converters with an 8-bit, 16-bit, 24-bit, or 32-bit resolution are commonly available. Some microcontrollers include analog-to-digital converters (ADC). Others provide digital-to-analog converters (DAC).  

RAM size, ROM size, and ROM type are important specifications to consider when selecting microcontrollers (MCU). Random access memory (RAM) can be read from or written to in a non-linear manner, but does not retain data when power is removed. Read-only memory (ROM) contains pre-programmed data, is either unchangeable or requires a special operation to overwrite, and retains data in memory when power is removed. There are several types of ROM. Mask ROM is a static form of memory that is programmed during fabrication with a special mask that contains the customer code. Erasable programmable read-only memory (EPROM) can be erased through exposure to ultraviolet light and then reprogrammed. Similarly, electrically erasable programmable read-only memory (EEPROM) can be erased electrically and then reprogrammed. Flash, a popular form of EEPROM, can be erased and reprogrammed in blocks instead of one byte at a time. Other types of ROM include factory advanced service technique read-only memory (FASTROM) and one-time programmed memory (OTP). 

General specifications for microcontrollers (MCU) include clock speed, interrupts, power characteristics, operating range, operating temperature, and life cycle stage. Clock speed, the maximum frequency, is measured in megahertz (MHz). Interrupts are asynchronous electrical signals that are transmitted from peripherals to a microprocessor. Power characteristics include supply voltage, supply current, and power dissipation. Some microcontrollers are suitable for commercial, industrial, or automotive applications. Others are designed for military specifications (MIL-SPEC). Operating temperature is a full-required range that is typically measured in degrees Celsius (C).  Life cycle stages for microcontrollers (MCU) range from introduction, rapid growth, and maturity to saturation, decline, phase out and removal.  

Microcontrollers (MCU) are available in a variety of integrated circuit (IC) package types and with different numbers of pins. Basic IC package types include ball grid array (BGA), pin grid array (PGA), land-grid array (LGA), chip-scale package (CSP), quad flat package (QFP), single in-line package (SIP), and dual in-line package (DIP). Many packaging variants are available. For example, BGA variants include plastic-ball grid array (PBGA), tape-ball grid array (TBGA), and multi-chip module plastic ball-grid array (MCM-PBGA). PGA variants include ceramic pin-grid array (CPGA) and plastic pin-grid array (PPGA). Common chip-scale packages are flip-chip chip scale package (FCCSP), stacked chip-scale package (SCSP), and ultra chip-scale package (UCSP). QFP variants include low-profile quad flat package (LQFP) and thin quad flat package (TQFP). DIPs are available in either ceramic (CDIP) or plastic (PDIP). Other IC package types for microcontrollers (MCU) include small outline package (SOP), thin small outline package (TSOP), and shrink small outline package (SSOP).

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Atmel Corporation - Industry Leader in the Design and... Microcontrollers AVR® 8-bit RISC AVR32 32-bit MCU AT91CAP Microcontrollers AT91SAM 32-bit ARM-based Microcontrollers See Atmel Corporation Profile & Catalog

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