KROHNE MFC 010 C Converter - Manual (Page 35)

MFC010 Interface Manual 33
7. MFC010 Modbus Data Model
7.1 MFC010 Register Structure
The register s tructure f or t he M FC010 begi ns w ith r egister 1001 in al l r egister t ypes ( Discrete O utput,
Discrete Input, Input Register and H olding Register). T he different variable types (integer, float, double
etc) have been arranged into groups of the same data type spread over the entire permitted register
address range.
It is not permissible, within this implementation of the MFC010 Modbus interface, to retrieve registers
containing different data types within the same request t elegram. A ttempts t o ac hieve t his w ill be
responded to with an “Illegal Data Address” exception error (See Section 5.6 on page 22).
Large gaps hav e been l eft bet ween t hese gr oups of dat a t ypes i n or der t o per mit ex pansion of the
MFC010 interface and compatibility with future high performance converters.
Data variables which require more than one register (e.g. a 4 byte “Float” requires two 2 byte registers to
transmit it) will occupy the number of consecutive registers needed to hold the variable. For example if a
floating point variable is contained in Register 3001, this will also fill register 3002. For this reason any
attempt t o r ead 3002 di rectly w ill be r esponded t o w ith an “Illegal Data Address” exception error ( See
Section 5.6 on page 22). This is the same for both Long Integers (which also require 2 consecutive 2 byte
registers to hold 4 bytes) and Double Precision Floating Point Numbers (which require 4 c onsecutive 2
byte registers to hold the 8 byte format of the Double Float).
In addition, when accessing these multi-register variables, the user must request the correct multiple of
registers. i .e. w hen ac cessing F loating P oint and Long i nteger v ariables, the number of registers
requested must be a multiple of 2, and when requesting Double Precision floating point variables the
number of registers requested must be a multiple of 4. Requesting variables with the incorrect multiple of
registers will again result in an “Illegal Data Address” exception error (See Section 5.6 on page 22). For
example if a request was made to a group of floating point variable register locations but only 3 registers
were requested, then the exception error would be returned.
Some of t he f ollowing r egisters ar e pr otected by t he “Service” password to prevent accidental or un-
authorised changes to key configuration values, specifically the sensor calibration settings, these registers
are indicated by the following symbol.

.
For details on t he operation and de -activation of the Service Password see section 8.5. Similarly, some
registers are protected by a Custody Transfer Password for use when the MFC010 is used in Custody
transfer applications, see section 8.9 on page 78. These registers are indicated by the
CT
symbol.
Holding registers marked
RO
are “Read Only”.
The following is a summary of the MFC010 register structure, the details of which are explained in the
following sections.