Alexander,

The previously mentioned 55 AA test is a good start but not fool proof. The problem is that you can get fooled if the part or your circuit has page addressing problems.

It is safer to write one pattern to all locations (say 55H) and then write a single location to AAH and then check all remaining locations to ensure that they still store a 55H. Then restore a 55H to this location and address the next and update it to AAH and perform the check again, continueing in this fashion until all locations have been tested. This does take some time.

I used this test to demonstrate a failed RAM when other swore the AA55 proved the RAM ok.

The above test is shortened version of the old "barber pole" ram check of yester-year when VLSI rams were far more faulty than today.