Accoulting document for price + discount sd billing doc

Hi,

There are two conditions in SD billing document

1) price ZP00 = 1000USD

2) discount ZD00 = 100USD

This condition has the same account determination rules. I tried two options

1) set the same ERL key

2) Set the same rules for ERL and ERS keys.

BUT in all cases I get two line for revenue acoount in FI document

1) +1000

2) -100

Is it possible to get +900 (price - discount) ?

Thank you for support.

Andrey