Statement List (STL) - DCE FEL ČVUT v Praze

Logic Control Instructions
6.19 LOOP Loop
Format
Description
Status word
LOOP
Address Description
Symbolic name of jump destination.
LOOP (decrement ACCU 1-L and jump if ACCU 1-L 0) simplifies
loop programming. The loop counter is accommodated in ACCU 1-L. The instruction
jumps to the specified jump destination. The jump is executed as long as the content
of ACCU 1-L is not equal to 0. 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).
BR CC 1 CC 0 OV OS OR STA RLO /FC
writes: - - - - - - - - -
Example for calculating the factor of 5
STL Explanation
L L#1 //Load the integer constant (32 bit) into ACCU 1.
T MD20 //Transfer the contents from ACCU 1 into MD20 (initialization).
L 5 //Load number of loop cycles into ACCU 1-L.
NEXT: T MW10 //Jump label = loop start / transfer ACCU 1-L to loop counter.
L MD20
* D //Multiply current contents of MD20 by the current contents of MB10.
T MD20 //Transfer the multiplication result to MD20.
L MW10 //Load contents of loop counter into ACCU 1.
LOOP NEXT //Decrement the contents of ACCU 1 and jump to the NEXT jump label if
ACCU 1-L > 0.
L MW24 //Program scan resumes here after loop is finished.
L 200
>I
Statement List (STL) for S7-300 and S7-400 Programming
6-20 A5E00706960-01