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Function Code
The function code field of a Modbus data unit is coded in one byte. Valid codes are
in the range of 1 ... 255 decimal (the range 128 - 255 is reserved and used or
exception responses). When a Modbus request is sent from a Modbus Client to a
Server device the function code field tells the Server what kind of action to perform.
The Modbus/TCP feature of OME-ET-7000/OME-PET-7000 series module supports
8 function codes, which allows the reading and writing of data contents of registers.
Function Code
01 (0x01)
02 (0x02)
03 (0x03)
04 (0x04)
05 (0x05)
06 (0x06)
15 (0x0F)
16 (0x10)
Any other function code request will be returned with an error response indicating
the function code is not supported, as well as a request for too much data or data at
a register address that not present.
Data
The data field of Modbus request sent from a client to server devices contains
additional information that the server uses to take the action defined by the function
code. This can include items like discrete and register addresses, the quantity of
items to be handled, and the count of actual data bytes in the field.
The data field may be nonexistent (of zero length) in certain kinds of requests; in this
case the server does not require any additional information. The function code alone
specifies the action.
Function
Read Coil Status
Read Input Status
Read Holding Registers
Read Input Registers
Force Single Coil
Preset Single Register
Force Multiple Coils
Preset Multiple Registers
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