6 handling of large data types – KROHNE ALTOSONIC V Modbus EN User Manual
Page 16
ALTOSONIC V
ModBus Manual 0300 rev07 E
7.30855.35.00
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6 HANDLING OF LARGE DATA TYPES
The standard Modbus specification does not explain how data types larger than 16 bits should be
handled. The standard Modbus functions to modify holding registers are used for handling larger data
types.
Function 03 (read multiple holding registers), function 06 (write single holding register), and function 16
(write multiple holding registers) are used to read or modify these data types.
In the UFP-V each register-area contains a data type.
In order to maintain compatibility with older systems, a parameter 5.2 MODBUS_MODICON_COMPAT
controls how the registers are counted.
In modicon compatible mode the data is counted as 16 bit registers.
In not-modicon compatible mode the data is counted on the data type, so a float is one register!
Notice that function 6 in not-modicon compatible mode will also write one type of the accompanying
data type!
The supported data types are:
•
Boolean
•
Integer (16 bit)
•
Long integer (32 bit)
•
Float (32 bit)
•
ASCII 8 characters (64 bit)
•
Double (64 bit)
•
ASCII 16 characters (128 bit)
The register ranges for each data type:
Number of registers to request for each data type
Function
Address
(default)
Data type
Modicon
compatible
Not Modicon compatible
1,2,5,15
1000..2999
Boolean
1
1
3000..3999
Integer
1
1
5000..5999
Long integer
2
1
6000..6999
Double
4
1
3,4,6,16
7000..7999
Float
2
1
4000..4999
ASCII (8 char)
4
1
3,16, 65, 66
14000..14999
ASCII (16 char)
8
1
Notice that in modicon compatible mode each data type larger than 16 bits should be addressed as 16
bit registers. For instance the first float is located on address 7000/7001 the next float is located on
address 7002/7003.
A double would be accessed by four 16-bit registers, so the first double 6000/6001/6002/6003 and the
next double 6004/6005/6006/6007.
The data in the chapter 8.4 Modbus Mapping Assignments is printed as it should be accessed in not-
modicon compatible mode and modicon compatible mode.