Understanding Smart Sensors - Nomads.usp

The Implications of Smart Sensor Standards 299Cost is a key enabler for many new systems. As software costs and developmenttimes continue to rise, many companies in the embedded-systemsworld are viewing Java as a program language that will let them write code onceand move easily from one MCU to another [2]. However, Java was developedfor desktop computing and has functionality that exceeds the requirements ofembedded control. Subsets of Java could prove to be the answer for more costcontroland memory-sensitive applications.The PC serial buses universal serial bus (USB) and IEEE 1394 (alsoknown as Firewire) provide plug-and-play and are expected to play a prominentrole in data acquisition (DA) [3]. Table 13.1 [3] compares those twoplug-and-play standards. As many as 127 devices can be connected to one USBTable 13.1USB Compared to Firewire for Data Acquisition (After: [3])Bus Pros ConsTheoreticalThroughputActualThroughputDistanceFrom PCISA busPCI busPC cardsEnhancedparallel portUniversalserial busFireWire(IEEE 1394)Large variety ofboards, extensivesoftware support,easy to writedrivers, costeffectiveboardsPlug-and-play,high-speed bustransfersSmall size—portabilityOutside the PC—noise immunityOutside the PC—noise immunity,true plug-and-playOutside the PC—noise immunity,high-speed transfers,automaticconfigurationSlow datatransfer,few plugand-playboardsLimited numberof PCI slotsin somecomputersLimited channelcount, noDMA supportLimited transferrates2–3 MBps 500–750 Ksps Internal132 MBps 80–100 MBps InternalMachinedependent500 Kspsburst200–300 Ksps Up to 30–50ft100 Kspscontinuous5 m/cableFound only innew purchase,limited datatransfer rates12 Mbps