The difference of a microcontroller from a microprocessor is often difficult to see. For one, the packaging and usage of the two are often similar, especially the low bit chips. However, Microcontrollers are more specific with its task. It does one thing well, unlike microprocessors that are more general purpose.
Here are some of the characteristics of microcontrollers that makes a chip a microcontrollers :
· Microcontrollers are embedded inside some other device, often in consumer products
· It is dedicated to one task and run one specific program. The program is stored in a ROM and generally doesn't change
· It is often a low power device
· A microcontroller has a dedicated input device and often (but not always) has a small LCD or LED display for output. It takes input from the device it is controlling and controls the device by sending signals to the different components of the device
· It is often small and low cost
· A microcontroller is often 'ruggedized' in some way, since it has to work in extreme conditions sometimes
As one writer puts it, a microcontroller is a computer on a single chip. It contains a CPU and a variety of peripherals to assist in its application.
Microcontrollers are often classified by the manner in which the program created for it is stored.
1. ROMless Microcontrollers are those with an external bus, which requires an EPROM or non-volatile SRAM for code storage.
2. An OTP microcontroller can be programmed exactly once. If the program is wrong, the chip will be thrown away and a new one is programmed again.
3. A masked microcontroller contains ROM that is factory-programmed. It is very cheap, especially when produced in large quantities.
4. Flash microcontrollers are quite novel. They operate similar to OTPs, but can be reprogrammed many times. It is more expensive than OTP, though.
Some of the popular microcontroller chips are :
· 8051 - first offered by Intel in the late 70's, this chip is at the heart of the biggest microcontrollers available. It has a Harvard architecture, its instruction cycle is 750 ns and generally clocks at 16 MHz. Philips is the biggest provider of 8051. Other players are Atmel and Dallas.
· Z8 - this is part of small OTP parts oriented at the low-cost consumer market. Cheap emulator is also available.
· AVR - this is a new chip touted as RISC. Instruction cycles only take 250 ns, around 4 times quicker than its direct competitor, the PIC.
· HC05 - this is Motorola's version for the low-end 8 bit market. It showcases Von Neumann architecture, although relatively slow.
· HC11 - this is ;ore powerful than HC05 and directly competes with 8051.
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