The program uses a CPU Clock memory, Setting MB100 clock memory, the M100.0 change cycle is 0.1s. Enter the symbol address As I0.1, I0.1 positive edge down counter C0 to set the number, if I0.0 is 1, C0 minus 1 per 0.1s. Output symbol address Q0.0.
The S7-300 Counter extension – Timer Programming Example
PLC ONE 