A2: Various NC/PLC interface signals and functions
1.3 Functions
Basic Functions
60
Function Manual, 09/2011, 6FC5397-0BP40-2BA0
Access from NC
To allow the NC to access PLC variables (from a part program) quickly, $ variables are provided in the NCK. The
PLC uses a function call (FC) to read and write $ variables. Data are transferred to and from the NCK
immediately.
$ variables can be accessed (by the NCK) during preprocessing and in synchronized actions.
Data type information is determined by the $ variable data type, the position index is specified as an array index
(in bytes).
The following $ variables are available:
Ranges of values
Access from PLC
The PLC uses function calls (FC) to access the memory. These FCs ensure that data are read and written in the
DPR immediately, i.e. not just at the beginning of the PLC cycle. FCs receive data type information and the
position offset as parameters.
Figure 1-9
Communications buffer (DPR) for NC/PLC communication
$A_DBB
Data byte (8 bits)
$A_DBW
Data word (16 bits)
$A_DBD
Data double word (32 bits)
$A_DBR
Real data (32 bits)
$A_DBB(n)
<= x <= 255
$A_DBW(n)
-32768 <= x <= 3276
$A_DBD(n)
-2147483648 <= x <= 2147483647
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3/&
1&
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