5 Implementation of Modbus TCP
5.6 The Service-Object
66
XI/ON: XNE-GWBR-2ETH-MB
10/2011 MN05002008Z-EN
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Supported service numbers:
A service request may have the following results:
5.6.1
Indirect reading of registers
1 to 122 (Count) Modbus-registers are read, starting with address x (Addr).
• service-request
• service-response
Table 15:
Supported
service
numbers:
Service code
Meaning
0×0000
no function
0×0003
indirect reading of registers
0×0010
indirect writing of registers
Table 16:
results of the
service request
Service code
Meaning
0×0000
error free execution of service
0×FFFE
service parameters incorrect/ inconsistent
0×FFFF
service code unknown
Note
The services "indirect reading of registers" and "indirect writing of registers" offer an
additional possibility to access any Modbus register.
Current Modbus-masters support only a limited number of register- areas that can
be read or written during the communication with a Modbus-server. These areas can
not be changed during operation.
In this case, the services mentioned above enables non-cyclic access to registers.
2000h
2001h
2002h
2003h
2004h
2005h
207Fh
service no.
0×0000
0×0003
Addr
Count
reserved
2080h
2081h
2082h
2083h
2084h
2085h
20FFh
service no. result
0×0003
Addr
Count
register contents