Understanding Smart Sensors - Nomads.usp

Communications for Smart Sensors 1356.7.1 CEBusThe consumer electronics bus (CEBus) was initiated by the Consumer ElectronicsGroup of the Electronic Industries Association (EIA). CEBus providesboth data and control channels and handles a maximum of 10 Kbps. It has agrowing acceptance in the utility industry [13].6.7.2 LonTalkThe acceptance of LonTalk in building automation, the availability of fullOSI layers, and interoperability are among the reasons that it is well suited forthe home automation environment. Simplicity and ease of installation are alsoimportant attributes, especially for add-on equipment. Widespread acceptancein other markets will also drive the learning curve for cost reduction that thismarket requires.6.8 Protocols in SiliconA few of the protocols discussed in this chapter have been implemented in siliconhardware and are available from multiple sources. In some cases, the protocolis a standalone integrated circuit. However, a protocol integrated into anMCU provides computing capability and a variety of system features that affectthe cost effectiveness of individual system nodes.6.8.1 MCU With Integrated SAE J1850A standard protocol provides sufficient volume potential for semiconductormanufacturers to design a variety of integrated circuits. In many cases, thehighly integrated solution provides the lowest cost per node. For example,Motorola’s MC68HC705V8, shown in Figure 6.7, integrates the J1850 communicationprotocol, on-chip voltage regulation, the physical layer interface,the J1850 digital aspect (VPW version), and other systems-related functions.The integrated solution has many features that make system design easier andreduce both component count and system cost.The heart of the J1850 chip is Motorola’s data link controller (MDLC),illustrated in Figure 6.8 [18]. The MDLC handles all communication duties,including complete message buffering, bus access, arbitration, and error detection[19]. Other J1850 versions have been implemented by a number ofsuppliers [20].