1710 HEIDENHAIN Technical Manual iTNC 530 HSCI
PGM CALL, including NC macros, and CYCL CALL (for cycles greater than 68) are
calculated automatically with the look-ahead function and run without exact
stop. At the beginning and end of the called program or cycle, it can happen
that a missing synchronization between machine status and look-ahead
calculation may lead to problems.
Example:
A TOOL CALL is run in look-ahead calculation. In this TOOL CALL a PLC function
is needed (e.g. opening the tool changer gate). The tool is automatically
changed on the machine. During this time the look-ahead calculation reaches
another TOOL CALL. Since the PLC function has been fulfilled (the tool changer
gate is open), the look-ahead calculation is continued. After the first tool
change has been completed, the PLC function is no longer fulfilled (the tool
changer gate is closed). The second TOOL CALL would be executed if the PLC
function were not fulfilled (the tool changer gate is closed).
The function FN20: WAIT FOR SYNC provides a remedy for this problem. If this
function is programmed at the beginning of an NC program (NC macro) or
cycle, in the look-ahead calculation the PGM CALL (NC-macro call) or CYCLE CALL
is not executed until the calling program has actually reached the PGM CALL
(NC-macro call) or CYCL CALL.
Look-ahead is halted for FN20: WAIT FOR SYNC, no matter at what point this
block is programmed.
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