Siemens SINUMERIK 840D sl Function Manual page 1505

Call example
1. Read double word of position offset 4 with semaphore in byte 0 and store in MD 100:
Data type Dword (4 bytes)
Position offset 4
CALL FC 21 (
UN M10.1;
R F10.0;
Examples of NCK programming from synchronized actions:
Data transfer from NC to PLC, with data written via synchronized actions;
Byte 0 serves as the semaphore
ID=1 WHENEVER $A_DBB[0] == 0 DO $A_DBR[4] = $AA_IM[X] $A_DBB[0] = 1
Data transfer from PLC to NC, with data read via synchronized actions;
Byte 1 serves as the semaphore
ID=2 WHENEVER $A_DBB[1] == 1 DO $R1 = $A_DBR[12] $A_DBB[1] = 0
Basic logic functions: PLC basic program solution line (P3 sl)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Enable := M 10.0,
Funct := B#16#3,
S7Var := P#M 100.0 DWORD 1,
IVAR1 := 4,
IVAR2 := 0,
Error := M 10.1,
ErrCode := MW12);
//Enable while 1, until value is read
Detailed description
2.12 Block descriptions
// if TRUE, FC 21 active
//Read data
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