Hi C4,
In the old days - we would physically turn the antiskid off when we only had accumulator pressure available. This was to prevent the antiskid system releasing & then reapplying the brakes, thus depleting the accumulator too quickly.
Now, Airbus logic will turn the antiskid off when you are down to accumulator pressure only. Thus you have about 7 brake applications available.
If you have Y hyd system pressure available, then you can make as many applications as you like with antiskid still working. The difference with Y system brakes is that there is only 1 antiskid sensor per tandem pair of wheels - and both wheel brakes on the same tandem pair are released when a skid is sensed. Thus it's not as effective as Green Sys brakes, where each individual wheel is sensed and each wheel brake is modulated individually.