KROHNE MFC 010 C Converter - Manual (Page 91)

MFC010 Interface Manual 89
10.3 “The MFC010 is responding with an Illegal Modbus Function Message”
There can be two reasons why this error response will be returned by the MFC010 in answer to a request.
a) The F unction bei ng r equested i s not valid f or t he M FC010, c heck t he l ist of v alid M odbus
functions in section 6 on page 23.
b) An attempt is being made to write to a password protected holding register. The password must
be de-activated before an attempt to write to the register is made. All registers are protected by
the Supervisor password when it is active. Those registers that are protected by the Service or
Custody Transfer passwords are indicated in the relevant sections of this document, see section
7.1 on page 33 for a s ummary. S ee s ection 8.5 on page 76 and section 8.9 on page 78 for
further details on the operation of the passwords.
10.4 “The MFC010 is responding with an Illegal Data Message”
When the MFC010 responds with an “Illegal data message”, it is because the value being written to a
holding register in the MFC1010 is beyond the permitted limits for that register, the limits for each holding
register are indicated in section 7.5.
10.5 “The MFC010 is responding with an Illegal Address Message”
There are four reasons why the MFC010 will return an “ Illegal Address” error message when the Master
device makes a request.
a) The register address being requested is not supported by the MFC010, check the requested
register against the register summary in section 7.1.
b) Although the Start address is valid, when accessing multiple registers the number of registers
requested may extend beyond the end of t he v alid addr ess r ange f or t hat gr oup of v ariables.
Check the number of variables requested and ensure that the last register address is valid.
c) The number of registers requested is not correct for the data type being requested. For example,
if registers containing floating point variables are r equested t hen t he num ber of r equested
registers m ust be a m ultiple of 2 as t he f loating poi nt v ariables ar e hel d i n t wo c onsecutive
registers. For Double precision floating point variables the number of registers requested must
be a multiple of 4.
d) From “c” above, the system will respond with an “Invalid Address” error when an attempt is made
to access the associated registers of a m ulti-register variable, for example when access to the
second register of a f loating point variable is attempted. i.e. if an attempt is made to access
Input register 3002, which contains the second half of the variable accessed by Input register
3001.