Hi,
You can go for event to set second field value. In GET_P method give event name, in that event handler method set the second field value.
GET_P method of first field.
CASE iv_property.
WHEN if_bsp_wd_model_setter_getter=>fp_fieldtype.
rv_value = cl_bsp_dlc_view_descriptor=>field_type_PICKLIST.
WHEN if_bsp_wd_model_setter_getter=>fp_server_event.
rv_value = 'SET_TEXT'.
ENDCASE.
in event EHON_SET_TEXT event set default value for second field.
Regards,
Deepika.