Modbus addressing is how a master picks out one device on a shared Modbus link, using a slave address (also called a unit ID). On a serial bus the address space has 256 addresses, and address 0 is reserved for broadcasts that every slave must recognise. The master needs no address of its own, but every slave needs one, and it must be unique on that serial bus. That is why installers program a unique Modbus address into each device. In the SMA Modbus profile, the unit ID is the top-level address. The profile has 247 unit IDs, and 245 of them can be assigned to individual devices. SMA reserves some unit IDs, such as 2 for system parameters and 3 for the inverter, and automatic system detection skips the reserved ranges. Register addressing is a separate layer. Within a device, registers are addressed from 0 to 0xFFFF, which gives 65536 addresses.
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part_ofAddressing rules are defined in the Modbus over serial line specification.
sec=2.2 h=4a57a8226320sec=2.2 h=4a57a8226320review note: support check: partial - Passages give the addressing rules under MODBUS, but nothing states they come from the serial line specification or that addressing is part of proto:modbus in that way.
related_toc2 drafted · lead SMA Modbus profile
SMA Modbus profile defines 247 unit IDs, 245 assignable to individual devices, with some IDs reserved.
sec=3.6.1 h=6e316b9706ddc3 drafted · lead Modbus TCP
ABB FENA module address mode maps inverter parameters to holding registers in the 0...65535 range.
sec=2.3 h=e02eab8fc342c4 drafted · lead Duplicate device bus address
Each slave address must be unique on a Modbus serial bus; installers set a unique Modbus address per device.
sec=2.2 h=4a57a8226320sec=2.2 h=4a57a8226320tbl=3.r9 h=5de0aac0ff5dreview note: support check: partial - Uniqueness of slave address on a serial bus is stated, but installers setting a unique address is only a table-of-contents heading, and duplicate-fault relation isn't stated.
related_to c3