8-bit microcontrollers

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Refreshing material Different processor architectures..

Microcontrollers Vs microprocessors

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Features of Different processor Architectures

CISCAddressing modes.Variable length inst.No. of clocks >1Less general purpose internal registersx86,8051

RISCLoad/store Architecture generally.Fixed length instructionGenerally inst.=1 clockMore general purpose internal registersPIC,ARM,AVR

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Address space architectureMemory is needed for programs and data.Program memory used in embedded systems is typically of non-volatile type.Data memory used is SRAM- or DRAM- type volatile memory.

Von Neumann-architecture:Program and data located in same address space.Harvard-architecture:Separate address spaces and buses for program and data memories.

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Harvard Vs Von Neumann

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ExamplesHarvard:8051Microchip PIC familiesAtmel AVRVon Neumann:PCs (Intel 80x86/Pentium) Motorola 68000 Motorola 68xx uC families

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Microprocessors Vs. MicrocontrollersA microprocessor (uP) is a one-chip CPU such as the Intel 80x86, or Pentium series, the Motorola 68000 series, the PowerPC series and so onThese single-chip systems were called microprocessors because they replaced an older generation which used multiple chips and even multiple pc boards to perform the same functions.A uP needs additional chips such as RAM, ROM, serial and parallel ports, timers, interrupt controllers and so on to make a complete cpu (motherboard).

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A microcontroller (uC) has the CPU and most, if not all of these peripheral functions built into a single chip.uCs tend to be much smaller than modern uPs, with memory in tens of bytes to kilobytes.uCs can also include other features such as oscillator-on-chip, A/D converters, reset circuitry, high current I/O drive capability, watchdog timers etc.

The benefit of uCs in embedded systems is that complete systems can be built with a very low component count, frequently just one chip.

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uPs have only one or two types of bit handling instructions whereas uCs have many such instructions.

uPs must have additional ports to be operational as a computer whereas uCs can function as a computer with no addition of external digital parts.

uPs have many opcodes for moving data from external memory to CPU whereas uCs have very few only one or two such instructions.

Programmers insight

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Reduce chip count.Many applications do not require as much computing power.Reduced power consumption.Reduced design cost

Why use a microcontroller?

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MicrocontrollersMicrocontrollers come as 4-bit , 8-bit , 16-bit and 32-bit.Expenses are represented by volume of package and number of pin count which further depend on basic data word-bit count, so as the data bits increase, cost of microcontroller increases.

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Useful for small computing tasks Adequate for many control and monitoring applicationsUsed in communications as serial ASCII data is also stored in byte size.Most integrated circuit memories arranged in an 8-bit configuration

Eight - Bit Microcontrollers

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Criteria for choosing a microcontrollerSpeed.Packaging.Power consumption.Amount of ROM and RAM.Number of I/Os and timers.Upgradation..Cost per unit.Availability of tools..& of microcontroller.

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