2.5 Modbus RTU: Function codes
BU 0050 GB-3111 Subject to technical amendments 65
2.5.4 03h Read Holding Register
This enables the readout of one or more parameters. However, usually only a single 16Bit format parameter
can be read out. The function code 0x10 must be used for 32Bit parameters.
The only exception to this are the process parameters P050 and P051. Here, all the elements of the array
assigned to the parameter can be read out simultaneously.
The parameter (P050) "Process data IN" and (P051) "Process data OUT" are executed in the
background and are not visible to the user. From a structural point of view, these are array
parameters ([-01 … -04]). Assignment of the setpoints in parameter (P050) is carried out via
the parameters (P546 (… P548)). The return of the actual values in parameter (P051) is
assigned in parameters (P543 (… P545)).
Example 1:
Parameter P102, parameter set 1 is read out (Content = 200 / 0x00C8).
Response (Slave Master)
Number of parameters High
Example 2:
The following 4 process data are read out: status word and actual values 1 to 3 (P051[-00] to P051[-03]) status
word = 0x2B37 // IW1 = 0x09C4 // IW2 = 0x0203 // IW3 = 0x09C4.
Response (Slave Master)
Number of parameters High
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