KROHNE ALTOSONIC V12 EN - Manual (Page 121)

MODBUS PROTOCOL DESCRIPTION AND SET-UP
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ALTOSONIC V12
www.krohne.com 04/2013 - 4002643502 - MA ALTOSONIC V12 R02 en
Exception codes (for example)
10.6 Handling of large data types
The standard Modbus specification does not explain how data types larger than 16 bits should be
handled. As larger data types are stored in a multiple of 16 bit registers, such data can be
accessed by means of “read” or “write” operation on a series of consecutive 16 bit registers.
Function 03 (read multiple holding registers), function 04 (read input registers), function 06
(write single holding register), and function 16 (write multiple holding registers) are used to read
or modify these data types.
Taking the data type into account, the addressing can be “optimized” accordingly, this is
implemented in an addressing mode not compatible with the original Modicon concept:
• In the original "Modicon compatible mode" one address is assigned and counted for each 16
bit register. To hold for example a 64-bit integer value, 4 addresses would be occupied.
Therefore, in order to address the next variable of this type, the address has to be
incremented by 4.
• In "not-Modicon compatible mode" addresses are incremented by 1 for each next variable.
For example, in order to read or write the next 64-bit variable, the register area to be read
will automatically be shifted by 4 16 bit registers
The ALTOSONIC V12 is by default configured for Modicon compatible addressing.
The supported data types are:
• Integer (16 bit)
• Long integer (32 bit)
• Float (single precision floating-point, 32 bit)
• Double (double precision floating-point, 64 bit)
• Long long (64 bit integer)
The register ranges for each data type:
Code Name Meaning
01 Illegal function The function code in
the request is not an
allowable action for
the slave.
02 Illegal data address The data address
received in the
request is not an
allowable address
for the slave.
Table 10-10: Exception codes