Siemens SINUMERIK 840D sl Function Manual page 165

Addressing with access to global variables
Index i always represents the distance in bytes from the beginning of the link memory. The
index is counted from 0. This means that:
Type
$A_DLB[i]
$A_DLW[i]
$A_DLD[i]
$A_DLR[i]
Link memory use
The link memory can have different assignments for processes that are completely
separated in time. The various NCU applications that access the link memory jointly at any
one time must use the link memory in a uniform way.
Access from synchronized actions
If an impermissible index is used for access to the link memory from a synchronized action
or a part program, alarm 20149 is issued.
Write access to link variables
When writing to link variables in a link memory of the type
$A_DLB[5]=21
for example, a write element is required. The write element serves for communication with
further NCUs which must see the modified contents in the link memory. Each write process
to a link variable requires a write element. It is busy with the write process until the main run
executing data exchange with the other NCUs is completed.
Since global data can be written by all channels and NCUs, the user must ensure proper
coordination of write and read access operations. Variables are written immediately if an
NCU link connection is active. Writing and immediate readback of a variable produces the
same result. Variables are written only in synchronism with the main run. Writing and
immediate readback in the same part program block produces a different result.
Extended Functions
Function Manual, 01/2008, 6FC5397-1BP10-3BA0
Several Operator Panels on Several NCUs, Distributed Systems (B3)
Interpretation of (i)
(The counting begins at 0 in each case)
Byte i is followed by a data of the byte type.
$A_DLB[7] addresses byte 8 from the beginning of the link memory.
Byte i is followed by a data of the word type.
$A_DLW[4] addresses the word which is located on byte 5 from the beginning of the
link memory.
Byte i is followed by a data of the double word type.
$A_DLD[12] addresses the double word which is located on byte 13 from the beginning
of the link memory.
Byte i is followed by a data of the real type.
$A_DLR[24] addresses the real value which is located on byte 25 from the beginning of
the link memory.
2.8 Cross-NCU user communication, link variables
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