Fixed Assets Depreciation Formula

Hi All

I have an asset with a life of 12 months.  The asset is being entered in JDE in Period  7  and we want to depreciate the asset for the first 7 periods on a straight line basis in Period 7 and then charge pro rata depreciation (1/12) also on a SL basis  from Period 8 to 12. 

For example if the asset costs $12,000:

I want the formula to do the following:

Period 7

<period when new asset is entered in the system>

-Calculate catch up depreciation expense  on a SL basis for 7 periods  - $7,000

Period 8 to Period 12

Calculate  pro-rata depreciation expense on an SL basis for each period - $1,000 per period.