1766-RM001A-EN-P MicroLogix 1400 Programmable Controllers ...

Communications Instructions 423The most significant digit of the address is considered a prefix, and doesnot get entered into the MB Data Address field when configuring themessage instruction.When the message is sent, the address is decremented by 1 and convertedinto a 4-character hex number to be transmitted via the network (with arange of 0-FFFFh); the slave increments the address by 1, and selects theappropriate memory group based on the Modbus function.TIPModbus protocol may not be consistently implemented in all devices. TheModbus specification calls for the addressing range to start at 1; however,some devices start addressing at 0.The Modbus Data Address in the Message Setup Screen may need to beincremented by one to properly access a Modbus slave’s memory,depending on that slave’s implementation of memory addressing.Local/Slave Node AddressThis is the destination device's node number if the devices are on aDH-485, DeviceNet (using 1761-NET-DNI), DF1, or Modbus network.TIPTo initiate a broadcast message on a DH-485, DF1 Half-Duplex, or DF1Radio Modem network, set the local node address to -1.To initiate a broadcast message on a Modbus network, set the slave nodeaddress to 0. Do not initiate more than one Modbus broadcast message ata time. When sequentially triggering multiple Modbus broadcastmessages, insert at least 10 msec. delay in between each message.Local/RemoteThis variable defines the type of communications that is used. Always uselocal when you need point-to-point communications via DF1 Full-Duplexor network communications such as Ethernet/IP, DeviceNet (using1761-NET-DNI), DF1 Half-Duplex, or DF1 Radio Modem. For DH-485, uselocal if the target node is on the same DH-485 network as this controller,or remote if the path to the target node goes through one or morecommunication bridges.Local MessagingExamplesFive examples of local messaging are shown in this section:• 500CPU message typePublication 1766-RM001A-EN-P - October 2008