Compare Two Values Afteredit

I have table reference with the following fields.
id (int)

name (varchar)

down (bit)

downdate (datetime)
I want after updating the value of each reference to check the status of the "down" field. if the value of "down" field is 1 then insert the current date in the "downdate" if the value of "down" is 0 then the field "downdate" left empty. I have written the following code using events and it gives the error.
if (values["Down"]==1)

{

values("DS_Down_Date")=now();

}

else

{

values("DS_Down_Date")=values ("")

}