Programming
10.9 Arithmetic parameters, LUD and PLC variables
Cylindrical grinding
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Programming and Operating Manual, 07/2009, 6FC5398-4CP10-2BA0
10.9.3
Reading and writing PLC variables
Functionality
To allow rapid data exchange between NC and PLC, a special data area exists in the PLC
user interface with a length of 512 bytes. In this area, PLC data are compatible in data type
and position offset. In the NC program, these compatible PLC variables can be read or
written.
To this end, special system variables are provided:
$A_DBB[n]
;Data byte (8-bit value)
$A_DBW[n]
;Data word (16-bit value)
$A_DBD[n]
;Data double-word (32-bit value)
$A_DBR[n]
;REAL data (32-bit value)
"n" stands here for the position offset (start of data area to start of variable) in bytes
Programming example
R1=$A_DBR[5]
;Reading a REAL value, offset 5 (starts at byte 5 of range)
Note
The reading of variables generates a preprocessing stop (internal STOPRE).
NOTICE
Writing of PLC tags is generally limited to a maximum of three tags (elements).
Where PLC tags are to be written in rapid succession, one element will be required per
write operation.
If more write operations are to be executed than there are elements available, then block
transfer will be required (a preprocessing stop may need to be triggered).
Example:
$A_DBB[1]=1 $A_DBB[2]=2 $A_DBB[3]=3
STOPRE
$A_DBB[4]=4
