Reference Manual

PMAC 2 Software Reference
PMAC Program Command Specification 357
For example, if the condition only needs to be checked every 20 msec and not every Real
Time Interrupt, you should consider using a DWELL command to regulate the execution
time of the WHILE loop.
WHILE ({condition})
DWELL20
ENDW
Example
WHILE (M11=0) WAIT ; Pause here until Machine Input 1 set
WHILE (M187=0) WAIT ; Pause here until all axes in-position
M1=1 ; Turn on Output 1 to activate punch
See Also
I-variable Ix28
Program commands DWELL, DELAY, STOP
WHILE({condition})
Function
Conditional looping
Type
Motion program (PROG only); PLC program
Syntax
WHILE ({condition})
WHILE ({condition}) {action}
where:
• {condition} consists of one or more sets of {expression} {comparator}
{expression}, joined by logical operators AND or OR.
• {action} is a program command.
Remarks
This statement allows repeated execution of a statement or series of statements as long as
the condition is true. It is PMAC’s only looping construct. It can take two forms:
1. (Valid in motion program only) With a statement following on the same line, it will
repeatedly execute that statement as long as the condition is true. No ENDWHILE is
used to terminate the loop.
WHILE ({condition}) {action}
2. (Valid in motion and PLC programs) With no statement following on the same line,
it will execute statements on subsequent lines down to the next ENDWHILE
statement.
WHILE ({condition})
{statement}
[{statement}
...]
ENDWHILE
If a WHILE loop in a motion program has no move, DWELL, or DELAY inside, PMAC
will attempt to execute the loop twice (while true) each real-time interrupt cycle (stopped
from more loops only by the “double-jump-back” rule), much like a PLC0. This can
starve the background tasks for time, possibly even tripping the watchdog timer. PMAC
will not attempt to blend moves through such an “empty” WHILE loop if it finds the loop
condition true twice or more.
In PLC programs, extended compound WHILE conditions can be formed on multiple
program lines through use of AND and OR commands on the program lines immediately
following the WHILE command itself (this structure is not available in motion programs).
Conditions in each program line can be either simple or compound. AND and OR
operations within a program line take precedence over AND and OR operations between
lines.