For-Next Loop Instructions - Siemens Simatic S7-200 System Manual

S7-200 Programmable Controller System Manual
For–Next Loop Instructions
Use the For (FOR) and Next (NEXT) instructions to delineate a loop
that is repeated for the specified count. Each For instruction requires
a Next instruction. You can nest For–Next loops (place a For–Next
loop within a For–Next loop) to a depth of eight.
The For instruction executes the instructions between the For and
the Next instructions. You specify the index value or current loop
count INDX, the starting value INIT, and the ending value FINAL.
The Next instruction marks the end of the FOR loop.
Error conditions that set ENO = 0
H 0006 (indirect address)
If you enable the For–Next loop, it continues the looping process
until it finishes the iterations, unless you change the final value from
within the loop itself. You can change the values while the For–Next
loop is in the looping process. When the loop is enabled again, it
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copies the initial value into the index value (current loop number).
The For–Next instruction resets itself the next time it is enabled.
For example, given an INIT value of 1 and a FINAL value of 10, the instructions between the For
instruction and the Next instruction are executed 10 times with the INDX value being incremented:
1, 2, 3, ...10.
If the starting value is greater than the final value, the loop is not executed. After each execution of the
instructions between the For instruction and the Next instruction, the INDX value is incremented and the
result is compared to the final value. If the INDX is greater than the final value, the loop is terminated.
If the top of stack is 1 when your program enters the For–Next loop, then the top of stack will be 1 when
your program exits the For–Next loop.
Table 6-55
Inputs/Outputs
INDX
INIT, FINAL
170
Valid Operands for the For and Next Instructions
Data Types Operands
INT IW, QW, VW, MW, SMW, SW, T, C, LW, AC, *VD, *LD, *AC
INT VW, IW, QW, MW, SMW, SW, T, C, LW, AC, AIW, *VD, *LD, *AC, Constant