1MDU07205-YN rev. F
REF601 CEI
User’s manual
77
7.4 Modbus RTU function codes
Table 1 & 2 below lists the Modbus RTU Function Code defi nitions, the maximum
number of registers allowed per request.
Table 1 : Modbus RTU function codes defi nitions
Function Code
Name Usage
Dec Hex
03 / 04 03/04
Read Holding
Registers /
Read Input
Registers
Read Data in 16-bit register format
( high / low). Used to read process
data. Registers are consecutive and are
imaged from the instrument to the host.
05 05
Change digital
output
Change the state of a digital output
06 06
Preset Single
Register
Write data in 16-bit integer format ( high
/low ) only.
08 08 Loop back Test
Used for diagnostic testing of the
communications port.
16 10
Preset Multiple
Registers
Write data in 16-bit format ( high / low ).
Used to write integer and fl oating point
override data. Registers are consecutive
and are imaged from the host to the
instrument.
70 46
Read Module
settings
Read baud rate, parity and relay
address settings.
Function Code
Maximum number of
resistors
Dec
Hex
03 03 16
04 04 16
05 05 04
08 08 08
Table 2 : Maximum number of resistors allowable per request
Serial Communication
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