How to create VAT tax voucher

Hi

We need to create a AP voucher in which the entire amount should be the accounted for tax (VAT).

Could  any one please guide me for the below

1. How to create a voucher for the scenario of Gross amount must be Tax amount.

2. Which tax explanation code I need to use to recognize the gross amount as tax amount

3. Do G/L distribution should be keep blank or need to be filled up?

4. Will the R09801 report create the tax entry automatically using the AAI (PT)

Thanks in Advance