From the RSLogix 500 help files:
Application note: You can write any value to S:4. It will begin incrementing from this value. You can use any individual bit of this word in your user program as a 50% duty cycle clock bit. Clock rates for S:4/0 to S:4/15 are: 20, 40, 80, 160, 320, 640, 1280, 2560, 5120, 10240, 20480, 40960, 81920, 163840, 327680, and 655360 ms The application using the bit must be evaluated at a rate more than two times faster than the clock rate of the bit.
RSLogix 500 - Copyright Rockwell Software 2000, 2001, 2002
So....
S:4/5 O:1/0
-] [----------( )-
O:1/0 would be on for .64 seconds and off for .64 seconds