Game of Life in a spread***?

I've heard that you can program the game of Life
in a spread***. How do you make progress in
discreet steps? How do you take a snapshot of
a generation, use it compute the next generation,
then (synchronously) overwrite the snapshot with
the new generation.

The problem I've having is that the spread***
tries to "compute everything at once". How do
I get it to stop to wait for the next generation.
How can I single step from one generation to the
next?

My question should be valid for all spreadsheets,
but the spread*** I'm using is OpenOffice Calc.
My questions aren't really about the game of Life,
they are about how to build cellular automata in
a spread***.

thanks
Bob Smith
.