Siemens SINUMERIK 840D sl Function Manual page 1093

2.12.2 FB 2: Read GET NC variable
Description of Functions
The PLC user program can read variables from the NCK area using FB GET. This function
block is capable of multi-instances and an instance-DB from the user area belongs to the FB
2.
When FB 2 is called with a positive signal edge change at control input "Req", a job is
started, which reads the NCK variables referenced by ADDR1ADDR8 and then copies them
to the PLC operand areas referenced by RD1 to RD8. Successful completion of the read
process is indicated by a logical "1" in status parameter NDR.
The read process lasts for several PLC cycles (normally 1-2). The block can be called up in
cyclic mode only.
Any errors are indicated by Error and State.
In order to reference the NC variables, all required variables are first selected with the "NC
VAR selector" tool and generated as STL source in a data block. A name must then be
assigned to this DB in the symbol table.
"DB name.S7 name" is transferred as the actual parameter of the NCK variable address
(Addr1 to Addr8) when FB 2 is called.
Variable addressing
For some NC-variables, it is necessary to select area no. and/or line or column from the NC-
VAR selector. A basic type can be selected for these variables,
i.e., area/column/line are preset to "0".
The contents of the area number, line and column specified by the NC VAR selector are
checked for a "0" in the FB. If a "0" is present, the value is transferred to the input parameter.
The user must supply the required parameters (UnitX/ColumnX/LineX) before calling FB
GET.
Here, unit corresponds to the area No., column to the column and line to the row.
Notice
FB 2 can read NC variables only
if basic program parameter NCKomm ="1" has been set (in OB 100: FB 1, DB 7). The call is
permitted only in cyclic program OB 1.
When channel-specific variables are read, in a task (FB 2-call)
via Addr1 to Addr8 only the variables of exactly one channel may be addressed.
In areas V and H, different logic axis numbers must not be assigned in one job. (Failure to
observe this rule results in Error:= TRUE, State:= W#16#02).
Basic logic functions: PLC Basic program powerline (P3 pl)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Detailed description
2.12 Block descriptions
109