Siemens SINUMERIK 840D sl Function Manual page 1381

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. The FB is
multi-instance-capable.
FB 2 also includes an Instance DB from the user area.
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.
FB PUT.
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 OB1. An assignment for all
parameters with Req = 0 is also permitted in OB100.
When channelspecific variables are read, only variables from one and the same channel
may be addressed via Addr1 to Addr8 in a job (FB 2 call).
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 solution line (P3 sl)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Detailed description
2.12 Block descriptions
107