NORD Drivesystems BU0050 - Manual (Page 65)

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.
NOTE
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)).
Master

Slave Slave

Master
Function Code 1 Byte 0x03 Function Code 1 Byte 0x03
Start address 2 Byte 0x0000 to 0xFFFF Number of bytes 2 Byte 0x01 to 0x08
Number of
parameters 2 Byte 0x0001 to 0x0004 Parameter value N*2Byte
Example 1:
Parameter P102, parameter set 1 is read out (Content = 200 / 0x00C8).
Query (Master

Slave) Response (Slave

Master)
Address 0x08 Address 0x08
Function Code 0x03 Function Code 0x03
Start address High 0x19 Number of bytes 0x02
Start address Low 0x80 Parameter value High 0x00
Number of parameters High 0x00 Parameter value Low 0xC8
Number of parameters Low 0x01 CRC High 0x65
CRC High 0x82 CRC Low 0xD3
CRC Low 0x27
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.
Query (Master

Slave) Response (Slave

Master)
Address 0x08 Address 0x08
Function Code 0x03 Function Code 0x03
Start address High 0x0C Number of bytes 0x08
Start address Low 0xC0 Parameter value 1 High 0x2B
Number of parameters High 0x00 Parameter value 1 Low 0x37
Number of parameters Low 0x04 Parameter value 2 High 0x09
CRC High 0x47 Parameter value 2 Low 0xC4
CRC Low 0xFC Parameter value 3 High 0x02
Parameter value 3 Low 0x03
Parameter value 4 High 0x09
Parameter value 4 Low 0xC4
CRC High 0x65
CRC Low 0xD3