Issue
Not all 3rd party manufacturers use the same Modbus addressing.
Product Line
Andover Continuum, EcoStruxure Building Operation
Environment
- Modbus RTU X Driver
- bCX1, CX controllers, NC2
- Building Operation Enterprise Server
- Building Operation Automation Server
Cause
Not all manufacturers use the same Modbus addressing.
Resolution
Many manufacturers have put their own slant on the "Modbus Standard" for addressing and number formats. The standard only defines 16 bit integer and binary data, but many manufacturers needed to use long integers (or swapped) and floating point numbers. They will transmit them as 2 integers over the protocol, then the receiving system needs to interpret them accordingly. To cope with this, special function codes were added which cover most formats.
There are various interpretations by different 3rd party systems on addressing. Some number from 0 and others starting at 1. Some require a 30000 or 40000 offset including in the address, depending on I/O type.
What is implemented in the X Driver is that whatever decimal address you enter in the X Driver point is what is sent down the bus. If the other system supplier is asked exactly what address they want sent down the bus, that is what is required in the X Driver point. Sometimes this is not the address that is on their datasheets. Sometimes there may be a need to add or subtract a value of 1, 30000 or 40000.
This article was written for Continuum, but is still relevant to EBO
Also see Helpful Modbus register Information for further information on Modbus registers.
