
B-63983EN/02 4.LADDER LANGUAGE
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4.15 NOTE ON PROGRAMMING
Some functional instructions may cause the ladder program to take a
long time to stop or make it unable to stop, if their ACT or RST
condition remains on for no apparent reason. If the ladder program
does not stop, all operations aimed at changing the ladder program will
take longer to end or will never end.
To avoid such problems, when you code a ladder program using
functional instructions, you need to design the ladder structure based
on a thorough understanding of the control conditions of the individual
instructions you use.
Listed below are typical cases in which the ladder program will not
stop.
• A low-speed window function is used for a WINDR or
WINDW functional instruction, and its ACT condition
remains on.
• In an EXIN instruction, its ACT condition remains on.
• In an AXCTL instruction, its ACT condition or RST
condition remains on.
• The jump destination label is present before a JMPB
instruction.
• In a JMPC instruction, the jump destination label points to
the same JMPC instruction.
If the ladder program takes long to stop or does not stop for any of these
reasons, the following operations will be affected.
1. Stopping the ladder program using a soft key on the screen
2. Reading a new ladder program from a memory card or other
medium, by using the data input and output screen
3 Updating the ladder program with changes made using the
ladder diagram edit screen
If any of the above phenomena occurs, the functional instruction
causing the problem needs to be fixed. Check the functional
instructions mentioned above to see whether there is any ACT or RST
condition remaining on, and correct the ladder program according to
the following procedure.
1. Put the machine in safe condition and turn off the power of
the NC.
2. Turn on the power of the NC while holding down the "CAN"
and "Z" keys simultaneously, to restart the NC with the
ladder program halted.
3. In the ladder diagram edit screen, redesign the logic
associated with the problematic functional instruction.
When done, set the ACT or RST condition to off. If the same
operation is repeating because of an inadequate JMPB or
JMPC instruction, review the jump condition and, if
necessary, change the ladder structure.