GB - 6
The following predefined ModBus functions are supported by the KEB ModBus interface:
• 3 : ‚Read Holding Registers‘
• 4 : ‚Read Input Registers‘
• 6 : ‚Preset Single Register‘
• 16 : ‚Preset Multiple Registers‘
At KEB functions 3 and 4 are completely identical.
The predefined ModBus functions are designed for word (16 Bit) data access. Addressing
of parameters is also done by 16 bit register address. Therefore this services can only
operate to the inverter with indirect set addressing (FR.09).
As some parameters of the KEB frequency inverter have 32 bit data length, additional
definitions had to be made for accessing those parameters. This problem has been
solved in two ways:
• First is that parameter access through functions 3, 4, 6, 16 in a certain register
address area is controlled by two mapping lists. One list for reading and another for
writing. With these lists it is possible to access as well as 16 bit or 32 bit parameters
with the functions 3, 4, 16. Also the direct set addressing is supported here. The
beginning of the register addresses of the mapping lists is programmable with
parameters MDB_MapStartAddr_Rd/Wr in the operator. The real length of the mapping
list is programmable with parameters MDB_MapNr_Rd/Wr in the operator. The
maximum length is limited to 100 (dec) words (16-Bit).
• Second is that two additional ModBus functions have been defined by KEB. The
ModBus specification [2] releases function codes for so called 'user defined function
codes‘. In this function area the following functions have been created:
• 100: Read Registers32: Reading several 32 bit registers (indirect set addressing
through FR.09))
• 101: Write Registers32: Writing several 32 bit registers (indirect set addressing through
FR.09)
2.3 ModBus Functions
ModBus
Reg-
Addr
Para-
Addr
Access controlled
by the mapping lists
0000h
0000h
1FFFh
2000h
5EFFh
5F00h
5FFFh
3EFFh
Parameter of the
frequency inverter
control
direct access
with Para-Addr =
Reg-Addr - 2000h
Operator Parameter
Read Mapping List
Write Mapping List
ModBus Functions
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