grid sorting only ascending and descending order

[Pra]

Hi All,

I want to sort my kendo grid columns only in "ascending" or "descending" order how can achive this.
i used below possible configurations. but i didn't get the expected behaviour.
1) "sortable: true" 
2) sortable: { mode: 'single' }, 
3) sortable: { mode: 'multiple' },


Thanks,
Praneeth.