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Installation and Configuration Manual 69
Modbus Communications
Calculated Parameters Modbus CommunicationsSafety CertificationFactory Default Settings Calculated Parameters Modbus CommunicationsSafety CertificationFactory Default Settings Calculated Parameters Modbus CommunicationsSafety CertificationFactory Default Settings Calculated Parameters Modbus Communications
Safety Certification
Factory Default Settings
Modbus byte ordering
Modbus register size
16-Bit register size (Register 48 = 00000000
16
)
In order to read 32-bit registers when Modbus registers are dealt with in units of 16 bits, you must
specify twice the number of 32-bit register you want to read in the ‘number of registers’ field. For
example, to read one 32-bit register, use '2'. If an attempt is made to read an odd number of registers,
the command will fail.
32-Bit register size (Register 48 = FFFFFFFF
16
)
In order to read 32-bit registers when Modbus registers are dealt with in units of 32 bits, you specify
the actual number of registers you want in the ‘number of registers’ field. (for example, to read two
32-bit register in this mode, use '2'.
D.4 Modbus register assignments
Each register is identified by a unique number, and the list is organized by this number. For each
register, the contents are described, along with the data type of the contents.
The data type is always 32 bits unless stated otherwise. Variable names are given for reference
purposes only. They have no other use.
Note: All units locations (registers 3, 4, 5 and 26) must be set before entering other values.
In some cases the data in a register is used to represent a non-numerical quantity, known as an index.
For example, the units of density can be kg/m
3
, gm/cc, lb/gal or lb/ft
3
and these are represented by the
numbers 91 to 94. Thus if Register 3 (line density) contains the value (index) 91, this means that the
units of line density are kg/m
3
. Index values may, of course, be used for more than one register.
Tables of these indices are given in Section D.5
Register 47 contents Modbus byte ordering
00000000
16
Big Endian (i.e. MSB first)
FFFFFFFF
16
Little Endian (i.e. LSB first)
Register 48 contents Modbus register size
00000000
16
16 bits
FFFFFFFF
16
32 bits
Table D-1 Modbus register assignments
Register Function Data Type
Index Table
(where
applicable)
0 API product type Long integer D.5.1
1 API referral reference temperature 4-byte float
2 API referral reference pressure 4-byte float
3 Line density units Long integer D.5.2