Siemens Simatic S7-300 Service Manual Page 82

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Logic Control Instructions
Statement List (STL) for S7-300 and S7-400 Programming
6-8
A5E00706960-01
6.7 JNB Jump if RLO = 0 with BR
Format
JNB <jump label>
Address Description
<jump label > Symbolic name of jump destination.
Description
If the result of logic operation is 0,
JNB <jump label>
interrupts the linear program
scan and jumps to a jump destination. The linear program scan resumes at the jump
destination. The jump destination is specified by a jump label. Both forward and
backward jumps are possible. Jumps may be executed only within a block, that is,
the jump instruction and the jump destination must lie within one and the same block.
The jump destination must be unique within this block. The maximum jump distance
is -32768 or +32767 words of program code. The actual maximum number of
statements you can jump over depends on the mix of the statements used in your
program (one-, two-, or three word statements).
If the result of logic operation is 1, the jump is not executed. The RLO is set to 1 and
the program scan continues with the next statement.
Independent of the RLO, the RLO is copied into the BR when there is a
JNB <jump
label>
instruction.
Status word
BR CC 1 CC 0 OV OS OR STA RLO /FC
writes: x - - - - 0 1 1 0
Example
STL Explanation
A I 1.0
A I 1.2
JNB JOVR //Jump if RLO = 0 to jump label JOVR. Copy RLO bit contents into the
BR bit.
L IW8 //Program scan continues here if jump is not executed.
T MW22
JOVR: A I 2.1 //Program scan resumes here after jump to jump label JOVR.
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