Digital Electronics: Principles, Devices and Applications

538 Digital Electronics13.6.1.2 Power consumptionPower consumption is an important factor for battery-operated systems. The power consumption of amicroprocessor varies with the supply voltage (square of supply voltage), speed (linearly) and withthe software the chip is running. The bus structure of the processor and its interconnection with thememory ICs should also be looked into.13.6.1.3 PerformanceProcessors that are good for one task may not be suitable for another. It is therefore very importantto define the processor requirements for the given application. These include the estimated size andcomplexity of the program, speed requirements (time-critical functions), the language to be used, thearithmetic functions needed, memory requirements (ROM, RAM and mass storage), I/O requirementsand interrupt source and response time required.After defining the application requirements, they should be matched with those that a processor canoffer. Table 13.1 enumerates the main parameters of the processor to be considered while selecting itfor a particular application.13.6.1.4 AvailabilityBefore zeroing onto a particular microprocessor, it is important to ensure that it is easily available.Table 13.1Microprocessor characteristics checklist.Instruction setRegister setAddressingBus and control signalsMiscellaneousNontechnical considerationsData types: bit operations, long wordsArithmetic functions: multiply and divideEncoding efficiency: RISC or CISCNumber of registersWidth of registersNumber of special-purpose registersNumber of modes: direct, indirect, etc.Segmented or linear addressingMemory and I/O address ranges (memory mapped/I/O mapped)Memory managementBus timingsInterruptsDMA/bus arbitration control signalsData and address bus widthClock speed and bus cycle timePrefetch (instruction queue length), cache memoryCoprocessor support: floating point, I/O processorsPower requirementsDocumentation quality and availabilityDevelopment tools: emulators, debuggers and logic analysersSoftware support: OS, compiler, assembler, utilities