B3: Distributed systems - 840D sl only
2.2 NCU link
Extended Functions
88 Function Manual, 03/2013, 6FC5397-1BP40-3BA1
2.2.2.1 Properties of the link variables memory
Parameterizing the memory size
The size of the link variables memory in bytes is set with the following machine data:
MD18700 $MN_MM_SIZEOF_LINKVAR_DATA (size of the link variables memory)
The setting for the size of the link variables memory should be identical for all NCUs involved
in the link group. If the memory sizes are different, the largest value assigned is used.
Initialization
After an NCU is powered up, the link variables memory is initialized with 0.
Structure
From the point of view of the system, the link variables memory is an unstructured memory
area that is available for link communication purposes. The link variables memory is
structured by the user/machine manufacturer alone. Depending on how the data structure is
defined, the link variables memory is accessed by means of data format-specific link
variables.
System-wide alignment
Once a link variables memory has been written to, the changes that have been made to the
data are transferred to the link variables memories of all other NCUs involved in the link
group. The link variables memories are usually updated by means of link communication
within two interpolation cycles.
2.2.2.2 Properties of the link variables
The link variables memory is accessed via the following data format-specific link variables:
Data type
1)
Designation Data format
2)
Bytes
2)
Index i
3)
Value range
UINT $A_DLB[ i ] BYTE 1 i = n * 1 0 ... 255
INT $A_DLW[ i ] WORD 2 i = n * 2 -32768 ... 32767
INT $A_DLD[ i ] DWORD 4 i = n * 4 -2147483648 ... 2147483647
REAL $A_DLR[ i ] REAL 8 i = n * 8 ±(2,2*10
-308
… 1,8*10
+308
)
1) Data type of link variables when used in part program/cycle
2) Data format of link variables or number of bytes addressed by the link variables in the link variables memory
3) The following must be noted for index i:
• Index i is a byte index that relates to the beginning of the link variables memory.
• The index must be selected so that the bytes addressed in the link variables memory are located on a data format limit
⇒ index i = n * bytes, where n = 0, 1, 2, etc.
–
$A_DLB[i]: i = 0, 1, 2, ...
–
$A_DLW[i]: i = 0, 2, 4, ...
– $A_DLD[i]: i = 0, 4, 8, ...
–
$A_DLR[i]: i = 0, 8, 16, ...
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