1771-6.5.132, PLC-5 DeviceNet Scanner User Manual

Before You Begin 1-7Communicating with YourPLC-5 ProcessorA block transfer read (BTR) isa block transfer of data fromthe 1771-SDN module to thePLC processor. The processoris reading the data collectedby the 1771-SDN module(i.e., DeviceNet input data).A block transfer write (BTW)is a block transfer of datafrom the PLC processor tothe 1771-SDN module. Theprocessor is writing the datato the 1771-SDN’s memory(i.e., DeviceNet output data).Your processor communicates with the 1771-SDN scanner module viablock transfer reads, block transfer writes, and DIO transfers.Input data, gathered from the network’s devices, is organized withinthe 1771-SDN and made available for the processor to “read”.The 1771-SDN module does not send data to your processor.Data transferred between the module and the processor must beinitiated by the processor. Output data is sent, or “written”, to thescanner by your processor. This data is organized in the 1771-SDNmodule, which in turn passes the data on to your scanned devices viastrobe, poll, change of state, or cyclic messages.PLC-5 ProcessorDiscrete Input ImageBA1Block Transfer Data FileCA2DEEI/O MapDiscrete I/OTransferBlockTransferRead1771-SDN ScannerInternal InputData StorageA1BCA2DEEInput fromthe devicesDiscrete Output ImageXBlock Transfer Data FileZYYYYDiscrete I/OTransferI/O MapBlockTransferWriteInternalOutput DataXYYYYZOutput tothe devicesPublication 1771-6.5.132 - June 2000