"Fehrenbach, Robert J" writes:
>The app notes for the 555 timer generally have a configuration using a
>single resistor which produces a 50% duty cycle.

        I stand corrected.  I don't have the application notes in
front of me, but I can almost imagine what the circuit looks like.  If
you place a resistance in series with a capacitor, the same time
constant applies for charging as for discharging so that  one should
get a 50% duty cycle if the capacitor is charged through the very same
resistor  that ultimately discharges it.

Martin McCormick