Employers get provided with a 'standing order' from HMRC when the base code (the amount of pay one can earn before any tax is paid) goes up - as it did last in April (as per Factor's info). So they normally do it automatically.
If yours is still less than 810, it may be because HMRC are aware that they need to claw back additional tax from you and they are doing this over the 2012/13 tax year by using a reduced code. Typical reasons for this are various but a common reason is that you owe tax from a previous year. But HMRC will only ever do this having informed you at the start of the year, in writing, as to what code applies to you.
As Factor says, if you have had communication from HMRC regarding your code, it is worth checking with the office that deals with you.