Siemens SIMATIC S7-400H Manual page 85

Example of STL
The requisite sections of the user program (OB1, OB 122) are listed below.
Table 6-1
STL
WBGA:
WBGB:
WBG0:
PZOK:
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
OB 1
Explanation
NOP 0;
SET;
R VERSUCH2; //Initialization
A BGA; //Read module A first?
JCN WBGB; //If No, continue with module B
SET;
R PZF_BIT; //Delete PZF bit
L PED 8; //Read CPU 0
U PZF_BIT; //Was PZF detected in OB 122?
JCN PZOK; //If No, process access OK
U VERSUCH2; //Was this access the second attempt?
JC WBG0; //If Yes, use substitute value
SET;
R BGA; //Do not read module A first any more
//in future
S VERSUCH2;
SET;
R PZF_BIT; //Delete PZF-Bit
L PED 12; //Read CPU 1
U PZF_BIT; //Was PZF detected in OB 122?
JCN PZOK; //If No, process access OK
U VERSUCH2; //Was this access the second attempt?
JC WBG0; //If Yes, use substitute value
SET;
S BGA; //Read module A first again in future
S VERSUCH2;
JU WBGA;
L ERSATZ; //Substitute value
//The value to be used is in Accumulator1
Using I/O on the S7-400H
6-13