siemens S7 high speed counters

Please help me !!! I am currently using a Siemens PLC the CPU is a 312C and i have a 100 pulse encoder wired into the 2 high speed inputs.
I wish to count the pulses in the program so my conveyor can stop at different positions but what logic do i require to make the counters work accuratley enough any suggestions please.

Try SFB47

Look in the Step 7 standard Libraries under system function blocks for SFB47 "COUNT". Highlight it and press F1 to get the help info and see if this is what you need. You will also need to go into the Hardware Configuration and setup the count portion of the CPU for counting. I haven't actually used these for counting but I have set them up similarly for measuring Frequency with SFB48 and noticed that there is a fair amount of configuration options under the Hardware Configuration.