The very first sentence of the Atmel 89c55WD datasheet is `Compatible with MCS-51 Products`and I certainly know that as you pointed out, this doesn`t mean a working code is necessarily works with another family product.

55WD is pin compatible with 51 and also applies same instruction set. No any speed differance or anything that affect the way they work. Only have some additional features.

But the problem is not if they are compatible or not.
It is why 55WD cannot make a read from ROM.

We`d better wait till I or Bahri try a read from 55`s ROM in assembler.

Rustu