Understanding Smart Sensors - Nomads.usp

Using MCUs/DSPs to Increase Sensor IQ 99Table 5.1Comparison of Semiconductor Memories (After: [4])FeRAMDRAMStatic RAM(SRAM) Flash EEPROMCell density* 3.5 2 5 1 4.5Nonvolatility Yes No No Yes YesRewrite speed 150~200 ns 50~100 ns 5~100 ns 10 ms~1 ms 1 msW/R endurance (W/R) Infinite Infinite (W/E) < 10 6 (W/E) < 10 510 10 ~10 13Power dissipation Very low Medium Medium Low MediumFeature inapplication*1 = smallest; 5 = largest.Battery backupequipmentHigh-densitymemoryHigh-speedmemoryFile and cardmemoryLow-densityNVROMevaluate the logic state of each input and drive outputs to logic 1 or 0 to implementthe control strategy. Input-capture and output-compare functions in theMCU simplify the design of the control strategy.Input-capture is used to record the time that an event occurred. Byrecording the time for successive edges on an input signal, software can determinethe period and the pulse width of the signal. Two successive edges of thesame polarity are captured to measure a period. Two alternate polarity edges arecaptured to measure a pulse width [5].Output-compare is used to program an action at a specified time. Forexample, an output is generated when the output-compare register matches thevalue of a 16-bit counter. Specific duration pulses and time-delay are easy toimplement with this function.5.3.4 Onboard A/D ConversionVarious types of ADCs were discussed in Chapter 4. An ADC is frequentlyintegrated with the MCU. For example, the typical ADC in the HC05 familyof MCUs consists of an 8-bit successive approximation converter and aninput-channel multiplexer. Some of the channels are available for input, andthe others may be dedicated to internal test functions. For example, the 8-bitADC of the MC68HC05B6 has a resolution of about 0.39%. The referencesupply for the converter uses dedicated input pins to avoid voltage drops that