Understanding Smart Sensors - Nomads.usp

166 Understanding Smart Sensorsembedded system has one or more computational devices (which may beMPUs or MCUs) that are not directly accessible to the user of the system. Arelatively new addition for computing requirements is the reduced instructionset computer (RISC) architecture. Computer and workstation manufacturersseeking the highest performance levels are using RISC architecture. Embeddedcomputing applications are also utilizing the performance that this approachprovides. The transition from CISC to RISC can be understood by analyzingthe following equation for MPU performance:Performance =MHz Instructions ClocksInstructions⋅ / (7.2)CISC-based architectures allocate transistors to decreasing the denominatorof (7.2) [25]. However, based on recent improvements in the price performanceof semiconductor memory and significant advances in compilertechnology, transistors can be reallocated to increasing the numerator. Thatis the basis of the RISC architecture that frees up transistors for integratingadditional components. The additional components can be peripherals ormicrocoded kernels that improve the performance in a specific application.Two approaches, CISC and RISC, are now available to solve a variety ofapplication problems in several markets. Because no single computing solutionis correct for all applications, designers must choose the approach that satisfiestheir design criteria. For a given application, there is a best-fit solution andmore than one feasible solution. CISC-based designs will continue to satisfy asignificant number of applications, especially in embedded control. However,RISC has established a credible presence in a range of commercial computingenvironments and its use will expand in embedded applications. RISC architecturein an embedded environment does not take advantage of the 64-bit bus,zero wait state memory, or the amount of memory integrated on one desktopMPU chip. To be affordable, the RISC performance is compromised but stillbeyond the capabilities of today’s CISC MCU.CISC MCUs range from simple 4-bit units and the most popular 8-bitunits up to 32-bit units. The lower cost versions are easily combined with singlesensors such as a pressure, flow, or acceleration sensor to provide a smart sensor.The high-performance 32-bit CISC and RISC units are allowing complexstrategies and diagnostics in automotive engine and powertrain control systems.They also are required for more complex sensing in imaging and navigationsystems.