jQuery Grid Plugin - jqGrid

Hi am hoping someone can help me, i have a jqgrid set up all is working nicely
i have a custom function to run when the edit/add form is submitted

the function geocodes an address from a postcode field,

once a postcode has been entered i want to poupulate other form fields with lattitude and longitude information from my geocode function.

Is it possible to target the fields in the form and set their values through my called function tehn submit the form

any ideas how/if this can be done?

I looked to see if this could be triggered on an onblur event for my postcode field, but couldnt find any info on how to do this.