On  a german usenet-list there have benn long long discussions about
similar problems with the AT89S8252. It seems that ATMEL "forgot" some
timing-values because some internal RCs are not  defined.

The thread-name : AT89S8252: Die ganze Wahrheit

maybe this helps a little bit....

>Testing our new Kit 123 - Atmel 89xxxx  programmer (Documentation on my
>website) we found a funny 'feature'.
>
>After Locking the Automatic detection feature looking for the signature
>bytes worked OK on an 89C51-24PC (the device was detected), but it did not
>work on an 89C51-20PC. Does anyone know why there might be a difference
>between the 20PC and 24PC in this way?
>
>Both chips worked quite OK. They were both properly programmed.
>

Michael Wieser
m.k.w@nextra.at

Service and Audiodesign