Many applications for custom macro B require the use of permanent common variables. These variables range in the #500 series and, of course, will not be lost when the machine’s power is turned off. So permanent common variables will remain until they are changed – much like tool offsets.
In some cases, the values of permanent common variables will seldom or never change. For example, probe manufacturers commonly use a series of permanent common variables to represent the calibration values for the probe.
Variables from #501 to #512, for example, may be used to represent overshoot-and-droop values and the probe’s stylus diameter. These variables, of course, are extremely important for probing. If they are mistakenly overwritten – possibly when someone unwittingly uses them in their own application, the results for probing will be disastrous.
A group of permanent common variables can be protected, much like programs in the O9000 series can be protected. If, after protecting some permanent common variables, someone tries to change one, an alarm will be sounded. This ensures that unchanging permanent common variables remain intact.
You must reference you Fanuc Operators manual to find the related parameters. It should be documented in the custom macro B section, near the description of permanent common variables. One parameter represents the value of the first permanent common variable to protect (setting this parameter to 500 will protect from #500). The other parameter specifies the value of the last permanent common variable to protect (setting this parameter to 512 will protect through #512). The value of the first parameter must, of course be less than or equal to the value of the second.