
Modbus RTU Function Codes
File Number
The file number word contains the register number from the register address structure shown in Table
Register Address
The register address is used to designate the tag ID number for the parameter being accessed. The register address is made up of two
Table 9-4 Register Address Format for Function Code 21
Register | Register | Format |
Address(es) | Address(es) |
|
(Dec) | (Hex) |
|
001 to 125 | 0001 to 007D | analog formatted data |
|
| (2 registers – IEEE |
128 to 215 | 0080 to 00D7 | integer formatted data |
& 255 | & 00FF | (2 registers – IEEE |
|
|
|
Unrestricted Registers
As mentioned previously, all register data is stored in the EEROM of this instrument with some exceptions. These exceptions were made to allow write access to override information. The registers, which are designated as Override values, are listed below. These registers do not have restrictions on the number of writes.
ID Tag | Register Number | UDC Usage |
125 | (7Dh) | Computer Setpoint |
Restrictions on Parameter Numbers in One Message
The maximum number of writeable parameters per write request is 1.
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