Generic Data source Delta issue

Hello Experts,

I Need help on delta functionality of generic data source.

we have created a function module based generic data source.

Created on date is used as delta reference field in RSO2.

But I read that we need to hard code the delta functionality in the function module itself.

The data source is working perfectly for full loads but delta load also its pulling full records.

can you tell me what code we need to put in the function module to extract delta.

Thanks,

Ankie