Detailed Description 
  2.12 Block descriptions 
PLC Basic Program Solution Line (P3 sl) 
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0 
2-207 
2. Read word of position offset 8 without semaphore and store in MW 104: 
 
CALL FC 21 ( 
  Enable :=  M 10.0,  // if True, FC 21 is active  
  Funct :=  B#16#3,  //Read data 
  S7Var :=  P#M 104.0 WORD 1,   
  IVAR1 :=   8,   
  IVAR2 :=  -1,   
  Error :=  M 10.1,   
  ErrCode :=  MW12);   
Function 
5: Update control signals to channel: 
The purpose of function 5 is to transmit important control signals at high speed in between 
cyclic data transfers. Data bytes 6 and 7 of user interfaces DB21 to DB30 are transferred to 
the NC. The channel is specified in parameter "IVAR1". This enable, for example, the feed 
disable, read-in disable to be transferred outside of the PLC cycle. 
The following signals are relevant: 
 
Signal  Type Type  Value range  Remarks 
Enable  I  Bool    1= FC 21 active 
Funct  I  Byte  5  5: Control signals to channel 
S7Var  I  Any  S7 data storage area  Not used 
IVAR1  I  Int  1. Max. channel  Channel number 
Error  Q  Bool     
ErrCode  Q  Int    1: "Funct" invalid 
10: Channel no. invalid 
6: Update control signals to axes: 
The purpose of function 6 is to transmit important control signals at high speed in between 
cyclic data transfers. Data byte 2 of application interface DB31 to DB61 is transferred to the 
NC. The transfer is performed for all activated axes. This allows the servo enable to be 
transferred outside the PLC cycle, for example. 
The following signals are relevant: 
 
Signal  Type Type  Value range  Remarks 
Enable  I  Bool    1= FC 21 active 
Funct  I  Byte  6  6: Control signals to axes 
S7Var  I  Any  S7 data storage area  Not used 
IVAR1  I  Int  0   
Error  Q  Bool     
ErrCode  Q  Int    1: "Funct" invalid