Brain Timing and "Latches"

[HimyKabibble]

I'm assuming brains are run periodically, like every pass through the main loop of Mach3?  I've become quite expert at writing brains that end up in endless loops, madly toggling things, or, in too many cases, hanging Mach completely, so I have to re-boot the machine.  Are brains evaluted/executed at a fixed time interval?  Is this why the "Timer" lobes are provided, to prevent race conditions?  If so, what is an appropriate delay to prevent races? 
Also, what does the "Latch" lobe function do?  I've found no explanation anywhere.
One last question - Are functions limited to arithmetic expressions, or can we use logical expressions as well?  For example, if I want to have a lobe output one of two numeric values, based on the value of a boolean input, how would I do that?

Regards,
Ray L.

[poppabear]

Brains runs with machs update loop.

you can do values, via formulas feed by booleen results into the formula.

scott