Siemens SITRANS F M MAGFLO series Operating Manual page 12

Modbus RTU RS-485
12
5. Modbus addressing model
Function code 16 (Write multiple registers)
General exceptions:
•
Writing less than 1 or more than 120 registers => Exception 3 (Illegal data value)
•
If ByteCount is not exactly 2 times NoOfRegisters => Exception 3 (Illegal data value)
•
Exceeding max. message size (25 registers) => Exception 2 (Illegal data address)
•
Writing data above/crossing limitation of max. register address (0xFFFF) => Exception 2
(Illegal data address)
Application exceptions:
•
Application errors => Exception 4 (Slave device error)
•
Further information about the error can be read from holding registers 682+683 (Last
HoldReg Addr + ErrorNo)
•
Application errors include writing to ReadOnly holding registers
Holes / register alignment:
•
If start-address is not the start of a mapped holding register => Exception 2 (Illegal data
address)
•
Writing to holes is allowed (ie ignored - and no exception occurs) - except for the condition
described above
•
If the end address is only part of a mapped holding register item (e.g. one half of a float value),
the action depends on the datatype. It is allowed to update first part of „VisibleString" and
„ByteArray" datatypes (although strange results may appear, if the VisibleSting does not
include the terminating zero). Writing parts of all other datatypes => Exception 4 (Slave device
error)
Function code 17 (Report Slave ID)
•
There are no exceptions for this function
Generally writing stops when the first exception occurs. When writing multiple registers, writing
starts with the register with the lowest address - and continues until an exception occurs - or until
all registers are updated.
SFIDK.PS.023.D2.02