Siemens S7-400 Service Manual download pdf (Page 219)

Working with Ladder Logic

Ladder Logic (LAD) for S7-300 and S7-400 Programming

A5E00706949-01

C-3

C.1.1 Adder with EN and with ENO Connected

If the adder has an EN and an ENO connected, the following STL instructions are

triggered:

1 A I 0.0 // EN connection

2 JNB _001 // Shift RLO into BR and jump if RLO = 0

3 L in1 // Box parameter

4 L in2 // Box parameter

5 +I // Actual addition

6 T out // Box parameter

7 AN OV // Error recognition

8 SAVE // Save error in BR

9 CLR // First check

10 _001: A BR // Shift BR into RLO

11 = Q 4.0

Following line 1 the RLO contains the result of the preceding logic operation. The

JNB instruction copies the RLO into the BR bit and sets the first check bit.

•

If the RLO = 0, the program jumps to line 10 and resumes with A BR. The

addition is not executed. In line 10 the BR is copied into the RLO again and 0 is

thus assigned to the output.

•

If the RLO = 1, the program does not jump, meaning the addition is executed.

In line 7 the program evaluates whether an error occurred during addition, this

is then stored in BR in line 8. Line 9 sets the first check bit. Now the BR bit is

copied back into the RLO in line 10 and thus the output shows whether the

addition was successful or not.

The BR bit is not changed by lines 10 and 11, so it also shows whether the

addition was successful.

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Siemens S7-400 Service Manual Page 219