Understanding Smart Sensors - Nomads.usp

Using MCUs/DSPs to Increase Sensor IQ 97to obtain information from sensors and control output devices. Some ofthe most common peripherals are general-purpose I/O ports, timers, and serialports.Timers usually measure time relative to the internal clock on the chip oran externally provided clock signal. An on-chip oscillator that operates up to4.0 MHz at 5V or 1 MHz at 3V controls the clock on the chip. A more complextimer can generate one or more PWM signals, measure the pulse width,and generate additional output pulse trains.Two basic serial ports are the serial communications interface (SCI) andthe serial peripheral interface (SPI). The SCI is a simple two-pin interface thatoperates asynchronously. Data is transmitted from one pin and received on theother. Start and stop bits synchronize communications between two devices.The SCI port is a universal asynchronous receiver transmitter (UART) that canbe used with an RS-232 level translator to communicate with personal or othertypes of computers over fairly long distances.The SPI port requires a third pin to provide the synchronizing signalbetween the control chip and an external peripheral. This type of communicationis usually on the same board. Standard SPI peripherals are available frommany manufacturers and include ADCs, display drivers, EEPROM, and shiftregisters.5.3.2 MemoryVarious types of memory can be integrated on a chip, including RAM, readonly memory (ROM), EPROM, EEPROM, and flash memory. Semiconductormemory is based on a single transistor or cell that is on or off to generate abit that is eithera1ora0.Memory is classified as either volatile or nonvolatile.Volatile memory is not stored when the power is disconnected to the MCU.Nonvolatile (NV) memory is stored when power is disconnected. The amountof memory in a chip is usually rated in kilobytes (1 KB = 1,024 bits). Increasingthe amount of memory increases the chip size and the chip cost. Some types ofmemory, such as EEPROM, can significantly increase the process complexityand also add to the cost.RAM can be read or written (changed) by the CPU and is volatile [3].The write/read (W/R) endurance is a key parameter for RAM. Dynamic RAMrequires a frequent refresh signal or the data will be lost. Static RAM does notrequire a refresh signal. ROM, which can be read but not changed, is nonvolatilememory and is included in the design (masked layout) of the chip. Reprogramminga chip once it has been designed is a common practice to correcterrors in the original software, to upgrade to improve system performance, or toadjust for variation that could have occurred since the system was initially