Understanding Smart Sensors - Nomads.usp

Communications for Smart Sensors 13926 kBytesflash192 kBytesflashPowerPCCPUQueuedADCL Bus12 kBytesSRAMQueuedADCBurstinterfaceL Bus10 kBytesSRAMQueued serialmultichannelmoduleU BusL-Bus toU-businterfaceCAN 2.0controllerU BussysteminterfaceunitU-Bus tointermodulebus interfaceExternalbusIntermodulebus 2Timeprocessorunit 3Dual-porttimerRAMTimeprocessorunit 3CAN 2.0controller18-ChannelmodularI/O systemFigure 6.10 Block diagram of an MPC555 PowerPC MCU, a chip that integrates two CANmodules and a number of additional system features. (PowerPC is a trademarkof International Business Machines.)6.8.3 Neuron® Chips and LonTalk ProtocolThe LonTalk protocol is an integral part of a Neuron IC, such as Motorola’sMC143150 or MC143120. 2 The Neuron IC is a communications and controlprocessor with an embedded LonTalk protocol for multimedia networkingenvironments, in which received network inputs are used to control processoroutputs. As shown in Figure 6.11, the MC143150 has three CPUs: one for themedia access control (MAC) processor, one for the network processor, and onefor the application processor [7].The MAC processor handles layers 1 and 2 of the ISO protocol stack.That includes driving the communications subsystem hardware as well as executingthe collision avoidance algorithm. This processor communicates withthe network processor using network buffers located in shared memory [12].The network processor implements layers 3 through 6 of the ISOstack. Network variable processing, addressing, transaction processing, auth-2. Neuron® is a registered trademark of Echelon Corporation.